Glial cells in neuronal development: recent advances and insights from Drosophila melanogaster

Gila outnumber neurons and are the most abundant cell type in the nervous system. Whereas neurons are the major carriers, transducers, and processors of information, glial cells, once considered mainly to play a passive supporting role, are now recognized for their active contributions to almost every aspect of nervous system development. Recently, insights from the invertebrate organism Drosophila melanogaster have advanced our knowledge of glial cell biology. In particular, findings on neuron-glia interactions via intrinsic and extrinsic mechanisms have shed light on the importance of gtia during different stages of neuronal development. Here, we summarize recent advances in understanding the functions of Drosophila glia, which resemble their mammalian counterparts in morphology and function, neural stem-cell conversion, synapse formation, and developmental axon pruning. These discoveries reinforce the idea that glia are substantial players in the developing nervous system and further advance the understanding of mechanisms leading to neurodegeneration.     

Differentiation of embryonic versus adult rat neural stem cells into dopaminergic neurons in vitro*☆

BACKGROUND：It has been reported that the conversion of neural stem cells into dopaminergic neurons in vitro can be increased through specific cytokine combinations. Such neural stem cell-derived dopaminergic neurons could be used for the treatment of Parkinson’s disease. However, little is known about the differences in dopaminergic differentiation between neural stem cells derived from adult and embryonic rats. OBJECTIVE： To study the ability of rat adult and embryonic-derived neural stem cells to differentiate into dopaminergic neurons in vitro. DESIGN： Randomized grouping design. SETTING： Department of Neurosurgery in the First Affiliated Hospital of Sun Yat-sen University. MATERIALS： This experiment was performed at the Surgical Laboratory in the First Affiliated Hospital of Sun Yat-sen University （Guangzhou, Guangdong, China） from June to December 2007. Eight, adult, male, Sprague Dawley rats and eight, pregnant, Sprague Dawley rats （embryonic day 14 or 15） were provided by the Experimental Animal Center of Sun Yat-sen University. METHODS： Neural stem cells derived from adult and embryonic rats were respectively cultivated in serum-free culture medium containing epidermal growth factor and basic fibroblast growth factor. After passaging, neural stem cells were differentiated in medium containing interleukin-1α, interleukin-11, human leukemia inhibition factor, and glial cell line-derived neurotrophic factor. Six days later, cells were analyzed by immunocytochemistry and flow cytometry. MAIN OUTCOME MEASURES： Alterations in cellular morphology after differentiation of neural stem cells derived from adult and embryonic rats; and percentage of tyrosine hydroxylase-positive neurons in the differentiated cells. RESULTS： Neural stem cells derived from adult and embryonic rats were cultivated in differentiation medium. Six days later, differentiated cells were immunoreactive for tyrosine hydroxylase. The percentage of tyrosine hydroxylase positive neurons was （5.6 ± 2.8）% and （17.8     

Rhesus monkey neural stem cell transplantation promotes neural regeneration in rats with hippocampal lesions

Rhesus monkey neural stem cells are capable of differentiating into neurons and glial cells.Therefore,neural stem cell transplantation can be used to promote functional recovery of the nervous system.Rhesus monkey neural stem cells(1×105 cells/μL) were injected into bilateral hippocampi of rats with hippocampal lesions.Confocal laser scanning microscopy demonstrated that green fluorescent protein-labeled transplanted cells survived and grew well.Transplanted cells were detected at the lesion site,but also in the nerve fiber-rich region of the cerebral cortex and corpus callosum.Some transplanted cells differentiated into neurons and glial cells clustering along the ventricular wall,and integrated into the recipient brain.Behavioral tests revealed that spatial learning and memory ability improved,indicating that rhesus monkey neural stem cells noticeably improve spatial learning and memory abilities in rats with hippocampal lesions.     

Differentiation of endogenous neural precursors following spinal cord injury in adult rats☆

BACKGROUND： Studies have shown that cell death can activate proliferation of endogenous neural stem cells and promote newly generated cells to migrate to a lesion site.
OBJECTIVE： To observe regeneration and differentiation of neural cells following spinal cord injury in adult rats and to quantitatively analyze the newly differentiated cells.
DESIGN, TIME AND SETTING： A cell biology experiment was performed at the Institute of Orthopedics and Medical Experimental Center, Lanzhou University, between August 2005 and October 2007.
MATERIALS： Fifty adult, Wistar rats of both sexes; 5-bromodeoxyuridine （BrdU, Sigma, USA）; antibodies against neuron-specific enolase, glial fibrillary acidic protein, and myelin basic protein （Chemicon, USA）.
METHODS： Twenty-five rats were assigned to the spinal cord injury group and received a spinal cord contusion injury. Materials were obtained at day 1, 3, 7, 15, and 29 after injury, with 5 rats for each time point. Twenty-five rats were sham-treated by removing the lamina of the vertebral arch without performing a contusion.
MAIN OUTCOME MEASURES： The phenotype of BrdU-labeled cells, i.e., expression and distribution of surface markers for neurons （neuron-specific enolase）, astrocytes （glial fibrillary acidic protein）, and oligodendrocytes （myelin basic protein）, were identified with immunofluorescence double-labeling. Confocal microscopy was used to detect double-labeled cells by immunofluorescence. Quantitative analysis of newly generated cells was performed with stereological counting methods.
RESULTS： There was significant cell production and differentiation after adult rat spinal cord injury. The quantity of newly-generated BrdU-labeled cells in the spinal cord lesion was 75-fold greater than in the corresponding area of control animals. Endogenous neural precursor cells differentiated into astrocytes and oligodendrocytes, however spontaneous neuronal differentiation was not detected. Between 7 and 29 d after spinal cord injury, newl     

Response of the sensorimotor cortex of cerebral palsy rats receiving transplantation of vascular endothelial growth factor 165-transfected neural stem cells

Neural stem cells are characterized by the ability to differentiate and stably express exogenous ge- nes. Vascular endothelial growth factor plays a role in protecting local blood vessels and neurons of newborn rats with hypoxic-ischemic encephalopathy. Transplantation of vascular endothelial growth factor-transfected neural stem cells may be neuroprotective in rats with cerebral palsy. In this study, 7-day-old Sprague-Dawley rats were divided into five groups： （1） sham operation （control）, （2） cerebral palsy model alone or with （3） phosphate-buffered saline, （4） vascular en- dothelial growth factor 165 ＋ neural stem cells, or （5） neural stem cells alone. The cerebral palsy model was established by ligating the left common carotid artery followed by exposure to hypox- ia. Phosphate-buffered saline, vascular endothelial growth factor ＋ neural stem cells, and neural stem cells alone were administered into the sensorimotor cortex using the stereotaxic instrument and microsyringe. After transplantation, the radial-arm water maze test and holding test were performed. Immunohistochemistry for vascular endothelial growth factor and histology using hematoxylin-eosin were performed on cerebral cortex. Results revealed that the number of vas- cular endothelial growth factor-positive cells in cerebral palsy rats transplanted with vascular endothelial growth factor-transfected neural stem cells was increased, the time for finding water and the finding repetitions were reduced, the holding time was prolonged, and the degree of cell degeneration or necrosis was reduced. These findings indicate that the transplantation of vascu- lar endothelial growth factor-transfected neural stem cells alleviates brain damage and cognitive deficits, and is neuroprotective in neonatal rats with hypoxia ischemic-mediated cerebral palsy.     

Aldynoglia cells and modulation of RhoGTPase activity as useful tools for spinal cord injury repair

A combined approach in spinal cord injury (SCI) therapy is the modulation of the cellular and molecular processes involved in glial scarring. Aldaynoglial cells are neural cell precursors with a high capacity to differentiate into neurons, promote axonal growth, wrapping and myelination of resident neurons. These important characteristics of aldaynoglia can be combined with speciifc inhibition of the RhoGTPase ac-tivity in astroglia and microglia that cause reduction of glial proliferation, retraction of glial cell processes and myelin production by oligodendrocytes. Previously we used experimental central nervous system (CNS) injury models, like spinal cord contusion and striatal lacunar infarction and observed that adminis-tration of RhoGTPase glycolipid inhibitor or aldaynoglial cells, respectively, produced a signiifcant gain of functional recovery in treated animals. The combined therapy with neuro-regenerative properties strategy is highly desirable to treat SCI for functional potentiation of neurons and oligodendrocytes, resulting in better locomotor recovery. Here we suggest that treatment of spinal lesions with aldaynoglia from neu-rospheres plus local administration of a RhoGTPase inhibitor could have an additive effect and promote recovery from SCI.     

嗅鞘细胞对神经干细胞增殖与分化的影响

BACKGROUND： Olfactory ensheathing cells can promote oriented differentiation and proliferation of neural stem cells by cell-secreted neural factors. OBJECTIVE： To observe the effect of olfactory ensheathing cells on the differentiation and proliferation of neural stem cells. DESIGN, TIME AND SETTING： Cytology was performed at the Department of Neurology, Tongji Medical College, Huazhong University of Science and Technology, China, from September 2007 to October 2008. MATERIALS： Mouse anti-nestin polyclonal antibody （Chemicon, USA）, mouse anti-glial fibrillary acidic protein （GFAP） IgG1, mouse anti-2＇, 3＇-cyclic nucleotide 3＇-phosphodiesterase （CNPase） IgG1, mouse anti-Tubulin Class-Ill IgG1 （Neo Markers, USA）, Avidin-labeled Cy3 （KPL, USA）, and goat anti-mouse IgGl： fluorescein isothiocyanate （FITC） （Serotec, UK） were used in this study. METHODS：Tissues were isolated from the embryonic olfactory bulb and subependymal region of Wistar rats. Serum-free DMEM/F12 culture media was used for co-culture experiments. Neural stem cells were incubated in serum-free or 5% fetal bovine serum-containing DMEM/F12 as controls. MAIN OUTCOME MEASURES： After 7 days of co-culture, neural stem cells and olfactory ensheathing cells underwent immunofluorescent staining for nestin, tubulin, glial fibrillary acidic protein, and CNPase. RESULTS： Olfactory ensheathing cells promoted proliferation and differentiation of neural stem cells into neuron-like cells, astrocytes and oligodendrocytes. The proportion of neuron-like cells was 78.2%, but the proportion of neurons in 5% fetal bovine serum DMEM/F12 was 48.3%. In the serum-free DMEM/F12, neural stem cells contracted, unevenly adhered to the glassware wall, or underwent apoptosis at 7 days. CONCLUSION： Olfactory ensheathing cells promote differentiation of neural stem cells mainly into neuron-like cells, and accelerate proliferation of neural stem cells. The outcome is better compared with serum-free medium or medium containing 5% fetal bovine serum.     

Evaluation of glial cell proliferation with non-invasive molecular imaging methods after stroke

Glial proliferation:For the last decades,glial cells have been wrongly believed to have a mere passive supporting role for neurons.Nevertheless,this notion has clearly changed and it is now admitted that these cells are essential for the correct development and regulation of the nervous system.Glia cell population are commonly subdivided in astrocytes,oligodendrocytes and microglia.During the development,neural stem cells(NSCs)(called neuroepithelial progenitor cells or NPCs)transform into radial glia,the primary progenitor cells for neurons,astrocytes and oligodendrocytes(Zuchero and Barres,2015).Microglial cells,however,derive from a mesenchymal precursor infiltration,meaning that during brain development,precursors generated in the bone narrow invade the nervous parenchyma and differentiate into microglial cells(Zuchero and Barres,2015).This proliferative capacity is preserved in the adult mammalian brain,and neurogenic NSCs are stored in two restricted regions of the central nervous system(CNS),the forebrain subventricular zone(SVZ)and the hippocampal dentate gyrus(subgranular zone).These cells continue to produce neurons and glial cells during the adulthood,being activated after certain signals and leaving the quiescent state(Urbán et al.,2019).This process,in which glial progenitor cells differentiate into mature glia during development and in the adult brain to maintain and regulate brain function,is called gliogenesis(Ardaya et al.,2020).     

Transplantation of placenta-derived mesenchymal stem cell-induced neural stem cells to treat spinal cord injury

Because of their strong proliferative capacity and multi-potency, placenta-derived mesenchymal stem cells have gained interest as a cell source in the field of nerve damage repair. In the present study, human placenta-derived mesenchymal stem ceils were induced to differentiate into neural stem cells, which were then transplanted into the spinal cord after local spinal cord injury in rats. The motor functional recovery and pathological changes in the injured spinal cord were observed for 3 successive weeks. The results showed that human placenta-derived mesenchymal stem cells can differentiate into neuron-like cells and that induced neural stem cells contribute to the restoration of injured spinal cord without causing transplant rejection. Thus, these cells promote the recovery of motor and sensory functions in a rat model of spinal cord injury. Therefore, human placenta-derived mesenchymal stem cells may be useful as seed cells during the repair of spinal cord injury.     

Cortical neurogenesis in adult rats after ischemic brain injury: most new neurons fail to mature

The present study examines the hypothesis that endogenous neural progenitor cells isolated from the neocortex of ischemic brain can differentiate into neurons or glial cells and contribute to neural regeneration. We performed middle cerebral artery occlusion to establish a model of cerebral ischemia/reperfusion injury in adult rats. Immunohistochemical staining of the cortex 1, 3, 7, 14 or 28 days after injury revealed that neural progenitor cells double-positive for nestin and sox-2 appeared in the injured cortex 1 and 3 days post-injury, and were also positive for glial fibrillary acidic protein. New neurons were labeled using bromodeoxyuridine and different stages of maturity were identified using doublecortin, microtubule-associated protein 2 and neuronal nuclei antigen immunohistochemistry. Immature new neurons coexpressing doublecortin and bromodeoxyuridine were observed in the cortex at 3 and 7 days post-injury, and semi-mature and mature new neurons double-positive for microtubule-associated protein 2 and bromodeoxyuridine were found at 14 days post-injury. A few mature new neurons coexpressing neuronal nuclei antigen and bromodeoxyuridine were observed in the injured cortex 28 days post-injury. Glial fibrillary acidic protein/bromodeoxyuridine double-positive astrocytes were also found in the injured cortex. Our findings suggest that neural progenitor cells are present in the damaged cortex of adult rats with cerebral ischemic brain injury, and that they differentiate into astrocytes and immature neurons, but most neurons fail to reach the mature stage.     

Significance of intercellular communication for neurodegenerative diseases

The nervous system is a highly complex organization composed of its basicunit,the neuronal cells,and specialized supporting cells,the glial cells.The main glial cells in the central nervous system(CNS)are astrocytes,microglia and oligodendrocytes.Astrocytes are the most abundant glial cell type in the CNS.     

Innate immune responses regulate morphogenesis and degeneration: roles of Toll-like receptors and Sarm1 in neurons

The central nervous system is recognized as an immunoprivileged site because peripheral immune cells do not typically enter it. Microglial cells are thought to be the main immune cells in brain. However, recent reports have indicated that neurons express the key players of innate immunity, including Toll-like receptors （TLRs） and their adaptor proteins （Sarml, Myd88, and Trif）, and may produce cytokines in response to pathogen infection. In the absence of an immune challenge, neuronal TLRs can detect intrinsic danger signals and modulate neuronal morphology and function. In this article, we review the recent findings on the involvement of TLRs and Sarml in controlling neuronal morphogenesis and neurodegeneration. Abnormal behaviors in TLR- and Sarml-deficient mice are also discussed.     

Axonal protein synthesis in central nervous system regeneration:is building an axon a local matter?

Neurons of the mature central nervous system(CNS,mainly the brain and spinal cord)are unable to regenerate spontaneously after a lesion,in contrast to neurons of the peripheral nervous system(PNS).While the extraneuronal environment was long thought to be limiting,evidence was given less than 15 years ago that neurons themselves are critical players of their own regeneration(Park et al.,2008).Indeed,CNS neurons show a decline of axon growth capacity as they mature and after an injury.Today,the role of axonal translation is actively explored in the paradigm of embryonic neuronal growth and in peripheral nerve injury and regeneration,but less is known about the role of local protein synthesis in regrowth of adult CNS axons.Here we discuss how the current understanding of axonal translation in the CNS may contribute to the development of novel strategies to enhance axon regeneration in the injured CNS.     

Human neural stem cells promote proliferation of endogenous neural stem cells and enhance angiogenesis in ischemic rat brain

Transplantation of human neural stem cells into the dentate gyrus or ventricle of rodents has been reportedly to enhance neurogenesis. In this study, we examined endogenous stem cell proliferation and angiogenesis in the ischemic rat brain after the transplantation of human neural stem cells. Focal cerebral ischemia in the rat brain was induced by middle cerebral artery occlusion. Human neural stem cells were transplanted into the subventricular zone. The behavioral performance of human neural stem cells-treated ischemic rats was significantly improved and cerebral infarct volumes were reduced compared to those in untreated animals. Numerous transplanted human neural stem cells were alive and preferentially localized to the ipsilateral ischemic hemisphere. Furthermore, 5-bromo-2′-deoxyuridine-labeled endogenous neural stem cells were observed in the subventricular zone and hippocampus, where they differentiated into cells immunoreactive for the neural markers doublecortin, neuronal nuclear antigen Neu N, and astrocyte marker glial fibrillary acidic protein in human neural stem cells-treated rats, but not in the untreated ischemic animals. The number of 5-bromo-2′-deoxyuridine-positive ? anti-von Willebrand factor-positive proliferating endothelial cells was higher in the ischemic boundary zone of human neural stem cells-treated rats than in controls. Finally, transplantation of human neural stem cells in the brains of rats with focal cerebral ischemia promoted the proliferation of endogenous neural stem cells and their differentiation into mature neural-like cells, and enhanced angiogenesis. This study provides valuable insights into the effect of human neural stem cell transplantation on focal cerebral ischemia, which can be applied to the development of an effective therapy for stroke.     

Collagen 1 signaling at the central nervous system injury site and astrogliosis

<正>Central nervous system(CNS)injuries are often devastating as functional recovery via axonal regrowth over the lesion site is very minimal.Failure of regeneration by injured CNS neurons is known to be due to both a reduced intrinsic regenerative capacity of adult neurons,as well as a non-permissive environment for axonal regrowth.In particular,the induction of astrogliosis and glial scar formation,which are prominently observed in brain and spinal cord injury(SCI)models,are widely assumed to contribute to both neuronal demise,as well     

Transplantation of olfactory ensheathing cells for promoting regeneration following spinal cord injury

OBJECTIVE： To investigate the status of olfactory ensheathing cells （OECs） transplantation in facilitating the regeneration of spinal cord injury. DATA SOURCES： Articles about OECs transplantation in treating spinal cord injury were searched in Pubmed database published in English from January 1981 to December 2005 by using the keywords of ＂olfactory ensheathing cells, transplantation, spinal cord injury＂. STUDY SELECTION： The data were checked primarily, literatures related to OECs transplantation and the regeneration of spinal cord injury were selected, whereas the repetitive studies and reviews were excluded. DATA EXTRACTION： Totally 43 articles about OECs transplantation and the regeneration and repair of spinal cord injury were collected, and the repetitive ones were excluded. DATA SYNTHESIS： There were 35 articles accorded with the criteria. OECs are the olfactory ensheathing glias isolated from olfactory bulb and olfactory nerve tissue. OECs have the characters of both Schwann cells in central nervous system and peripheral astrocytes. The transplanted OECs can migrate in the damaged spinal cord of host, can induce and support the regeneration, growth and extension of damaged neuritis. Besides, transgenic technique can enable it to carry some exogenous genes that promote neuronal regeneration, and express some molecules that can facilitate neural regeneration, so as to ameliorate the internal environment of nerve injury, induce the regeneration of damaged spinal cord neurons, which can stimulate the regeneration potential of the damaged spinal cord to reach the purpose of spinal cord regeneration and functional recovery. CONCLUSION： OECs are the glial cells with the energy for growth at mature phase, they can myelinize axons, secrete various biological nutrition factors, and then protect and support neurons, also facilitate neural regeneration. OECs have been successfully isolated from nasal olfactory mucosa and olfactory nerve. Therefore, autologous transplantation of OECs and objective genes modified OECs carrying various neurotrophic factors may become an effective method to treat spinal cord injury in the future.     

Differentiation of mesenchymal stem cells into neuronal cells on fetal bovine acellular dermal matrix as a tissue engineered nerve scaffold

The purpose of this study was to assess fetal bovine acellular dermal matrix as a scaffold for supporting the differentiation of bone marrow mesenchymal stem cells into neural cells following induction with neural differentiation medium.We performed long-term,continuous observation of cell morphology,growth,differentiation,and neuronal development using several microscopy techniques in conjunction with immunohistochemistry.We examined specific neuronal proteins and Nissl bodies involved in the differentiation process in order to determine the neuronal differentiation of bone marrow mesenchymal stem cells.The results show that bone marrow mesenchymal stem cells that differentiate on fetal bovine acellular dermal matrix display neuronal morphology with unipolar and bi/multipolar neurite elongations that express neuronal-specific proteins,including βIII tubulin.The bone marrow mesenchymal stem cells grown on fetal bovine acellular dermal matrix and induced for long periods of time with neural differentiation medium differentiated into a multilayered neural network-like structure with long nerve fibers that was composed of several parallel microfibers and neuronal cells,forming a complete neural circuit with dendrite-dendrite to axon-dendrite to dendrite-axon synapses.In addition,growth cones with filopodia were observed using scanning electron microscopy.Paraffin sectioning showed differentiated bone marrow mesenchymal stem cells with the typical features of neuronal phenotype,such as a large,round nucleus and a cytoplasm full of Nissl bodies.The data suggest that the biological scaffold fetal bovine acellular dermal matrix is capable of supporting human bone marrow mesenchymal stem cell differentiation into functional neurons and the subsequent formation of tissue engineered nerve.