Differential expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 in a scarring and nonscarring model of CNS injury in the rat

Injury to the adult brain results in abortive axon regeneration and the deposition of a dense fibrous glial scar. Therapeutic strategies to promote postinjury axon regeneration are likely to require antiscarring strategies. In neonatal brain wounds, scar material is not laid down and axons grow across the lesion site, either by de novo growth or regeneration. To achieve the therapeutic goal of recapitulating the nonscarring neonatal response in the injured adult, an understanding of how ontogenic differences in scarring reflect developmental diversities in the trophic response to injury is required. Fibrobast growth factor-2 (FGF-2) expression is developmentally regulated and has been implicated as a regulator of the wounding response of the adult rat central nervous system. We have investigated the expression of FGF-2 and fibroblast growth factor receptor 1 (FGFR1) after penetrating lesions to the cerebral cortex of 5 days post partum (dpp) (nonscarring) and 16 dpp and adult (scarring) rats. In situ hybridization, immunohistochemistry and Western blotting showed robust and sustained increases in FGF-2 and FGFR1 mRNA and protein in reactive astrocytes around the lesion in scarring rats, a response that was attenuated substantially in the nonscarring neonate. These results demonstrate that changes in astrocyte FGF-2 and FGFR1 expression are coincident with the establishment of a mature pattern of glial scarring after injury in the maturing central nervous system, but it is premature to infer a causal relationship without further experiments.     

Modulating astrogliosis after neurotrauma

Traumatic injury to the adult central nervous system (CNS) results in a rapid response from resident astrocytes, a process often referred to as reactive astrogliosis or glial scarring. The robust formation of the glial scar and its associated extracellular matrix (ECM) molecules have been suggested to interfere with any subsequent neural repair or CNS axonal regeneration. A series of recent in vivo experiments has demonstrated a distinct inhibitory influence of the glial scar on axonal regeneration. Here we review several experimental strategies designed to elucidate the roles of astrocytes and their associated ECM molecules after CNS damage, including astrocyte ablation techniques, transgenic approaches, and alterations in the deposition of the ECM. In the short term, mediators that modulate the inflammatory mechanisms responsible for eliciting astrogliotic scarring hold strong potential for establishing a favorable environment for neuronal repair. In the future, the conditional (inducible) genetic manipulation of astrocytes holds promise for further increasing our understanding of the functional biology of astrocytes as well as opening new therapeutic windows. Nevertheless, it is most likely that, to obtain long distance axonal regeneration within the injured adult CNS, a combinatorial approach involving different repair strategies, including but not limited to astrogliosis modulation, will be required.     

Penetration of grafted astrocytic scars by regenerating optic nerve axons in xenopus tadpoles

The following study was performed in order to determine the effect of a dense glial scar upon the outgrowth of neurites in the regenerating optic nerves of Xenopus tadpoles. Glial scars, primarily comprised of hypertrophic astrocytes, were formed in the optic nerves of postmetamorphic, juvenile Xenopus by unilateral enucleation. After 25–40 days, segments of glial scar tissue were then grafted near the cut retinal stumps of the transected optic nerves in stage 54–56 tadpoles. Within 7–10 days bundles of unmyelinated axons were seen among the cytoplasmic processes of the implanted astrocytes, and many of the fibers had traversed the entire extent of the graft by 7–10 days. The results indicate that in this regenerating system an extremely dense glial scar, formed by mature, hypertrophic astrocytes, does not represent a major obstacle to axonal outgrowth. These observations are discussed in relation to the problem of glial scarring and the general failure of regeneration in the mammalian central nervous system.     

Contact spacing among astrocytes in the central nervous system: an hypothesis of their structural role

Astrocytes are found throughout the central nervous system. They interact closely with surrounding structures, their processes contributing to the glia limitans of the neural tube, and to the glial investment of blood vessels, and of the somas, axons, and synaptic structures of neurones. This paper presents evidence that astrocytes in the central nervous system also interact with each other in a dual way, adhering to their neighbours via their processes, and repelling the somas of those neighbours. We suggest that this interaction, which has been termed contact spacing, distributes astrocytes through the central nervous system, and forms the basis of their structural role.     

Characteristics of fish glial cells in culture: possible implications as to their lineage.

Regeneration of injured central nervous system axons is largely dependent on the response of the associated nonneuronal glial cells to injury. Glial cells of the mammalian central nervous system, unlike those of fish, are apparently not conducive to axonal regeneration. While the lineage of rat glial cells is well characterized and its role in the support or inhibition of regenerative growth is beginning to be understood, little is known about fish glial cells. Accordingly, glial cells in cultures of adult goldfish brain and of newly hatched goldfish larvae were studied in an attempt to establish their lineage. The cells were identified by means of indirect immunofluorescence, using antibodies against fish astrocytes and oligodendrocytes. The cell count in the cultures increased from a small number of cells at 24 h after plating to a large number of both astrocytes and oligodendrocytes after 1 week in culture. Both of these cell types had originated from proliferating cells, as shown by their uptake of tritiated thymidine and by the inhibition of cell proliferation by 5-fluoro-2'-deoxyuridine. Both astrocytes, i.e., glial fibrillary acidic protein-positive cells, and oligodendrocytes, i.e., 6D2-positive cells, were positively labeled also by A2B5 antibodies, which are known to label progenitors of type-2 astrocytes and oligodendrocytes in the rat optic nerve. The results suggest that A2B5 positive progenitor cells in the goldfish central nervous system, as in the rat optic nerve, might be a common progenitor of astrocytes and oligodendrocytes.     

Novel insights into the glia limitans of the olfactory nervous system

Olfactory ensheathing cells (OECs) are often described as being present in both the peripheral and the central nervous systems (PNS and CNS). Furthermore, the olfactory nervous system glia limitans (the glial layer defining the PNS–CNS border) is considered unique as it consists of intermingling OECs and astrocytes. In contrast, the glia limitans of the rest of the nervous system consists solely of astrocytes which create a distinct barrier to Schwann cells (peripheral glia). The ability of OECs to interact with astrocytes is one reason why OECs are believed to be superior to Schwann cells for transplantation therapies to treat CNS injuries. We have used transgenic reporter mice in which glial cells express DsRed fluorescent protein to study the cellular constituents of the glia limitans. We found that the glia limitans layer of the olfactory nervous system is morphologically similar to elsewhere in the nervous system, with a similar low degree of intermingling between peripheral glia and astrocytes. We found that the astrocytic layer of the olfactory bulb is a distinct barrier to bacterial infection, suggesting that this layer constitutes the PNS–CNS immunological barrier. We also found that OECs interact with astrocytes in a similar fashion as Schwann cells in vitro. When cultured in three dimensions, however, there were subtle differences between OECs and Schwann cells in their interactions with astrocytes. We therefore suggest that glial fibrillary acidic protein–reactive astrocyte layer of the olfactory bulb constitutes the glia limitans of the olfactory nervous system and that OECs are primarily “PNS glia.”     

Pannexin 1在癫癎发病机制中的作用研究进展

癫癎是神经系统的常见疾病,其发病机制非常复杂,迄今未完全阐明。中枢神经系统内数量最多的星形胶质细胞及胶质细胞与神经元之间的主要连接方式是缝隙连接。Pannexins是最新发现的缝隙连接蛋白家族,在哺乳动物的中枢神经系统中广泛表达。多项研究提示Pannexin 1可能参与了癫癎的发病,本文就Pannexin 1在癫癎发病机制中的作用做一综述,为癫癎发病机制的研究提供参考。     

Substance P stimulates IL-1 production by astrocytes via intracellular calcium.

There is increasing evidence that local substance P (SP) exacerbates peripheral inflammations, partly by stimulating production of inflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha). SP may play similar roles in certain central nervous system inflammations. Multiple sclerosis plaques, for example, form around veins which are innervated by unmyelinated SP-containing fibers, and astrocytes in multiple sclerosis plaques stain for SP. We tested whether SP could stimulate IL-1 and TNF alpha production by cultured astrocytes and whether calcium was the second messenger in this process. We found that both SP and the calcium ionophore A23187 raised intracellular calcium ([Ca2+]i) and stimulated IL-1 production in astrocytes. SP also nonsignificantly increased TNF alpha production by astrocytes. Treatment with dibromo BAPTA/AM, an intracellular calcium buffer, blocked SP-induced IL-1 production. These findings indicate that SP induces IL-1 production by astrocytes and uses calcium as a second messenger. Our results indicate local SP may play a role in multiple sclerosis and certain other central nervous system inflammations.     

Central nervous system susceptibility to herpes simplex infection.

Four days after inoculation of herpes simplex virus (HSV) on the rabbit cornea, distinctive and reproducible lesions appear in the trigeminal root entry zone. These viral lesions, situated in the central nervous system (CNS) portion of the root, consist of severe myelin destruction accompanied by mononuclear cell infiltration and partial sparing of axons. Immunofluorescent study demonstrated abundant viral antigen, and by electron microscopy viral nucleocapsids were found to be numerous within astrocytes and were rarely found in other cell types. In contrast, the adjacent peripheral nervous system (PNS) tissue appears unaffected by the presence of virus. The mechanism for this marked difference in response of the central nervous system and the peripheral nervous system may depend upon the susceptibility of astrocytes to viral infection and replication. The selective nature of the lesion provides an easily reproducible model for further investigation of the response of nervous system tissue to HSV.     

An update on human astrocytes and their role in development and disease

Human astrocytes provide trophic as well as structural support to the surrounding brain cells. Furthermore, they have been implicated in many physiological processes important for central nervous system function. Traditionally astrocytes have been considered to be a homogeneous class of cells, however, it has increasingly become more evident that astrocytes can have very different characteristics in different regions of the brain, or even within the same region. In this review we will discuss the features of human astrocytes, their heterogeneity, and their generation during neurodevelopment and the extraordinary progress that has been made to model these fascinating cells in vitro, mainly from induced pluripotent stem cells. Astrocytes' role in disease will also be discussed with a particular focus on their role in neurodegenerative disorders. As outlined here, astrocytes are important for the homeostasis of the central nervous system and understanding their regional specificity is a priority to elucidate the complexity of the human brain.     

Expression and modulation of HLA-DR on cultured human adult astrocytes

Expression of Class II major histocompatibility complex (MHC) antigens on astrocytes has been implicated as contributing to the immune responses characteristic of chronic autoimmune diseases of the central nervous system. We examined the properties and regulation of HLA-DR on cultured human adult astrocytes. We found that a proportion of human astrocytes from each of fifteen individual donors expressed HLA-DR under basal culture condition; while this proportion differed among the human subjects (range 3-65%), the results for each individual remained relatively constant when analyzed at several time points (up to 125 days in vitro). Attempts to modulate HLA-DR expression by a variety of cytokines likely to be present in inflammatory infiltrates in the brain showed that only gamma-interferon could increase the proportion of human astrocytes that expressed HLA-DR. Whether the variability of HLA-DR expression on astrocytes between different individuals reflects a genetic trait which can influence susceptibility to autoimmune central nervous system diseases remains to be determined.     

N-cadherin influences migration of oligodendrocytes on astrocyte monolayers

Oligodendrocyte cell migration is required for the development of the nervous system and the repopulation of demyelinated lesions in the adult central nervous system. We have investigated the role of the calcium-dependent adhesion molecules, the cadherins, in oligodendrocyte-astrocyte interaction and oligodendrocyte progenitor migration. Immunostaining demonstrated the expression of N-cadherin on the surfaces of both oligodendrocytes and astrocytes, and oligodendrocyte-like cells adhered to and spread on N-cadherin substrates. The blocking of cadherin function by antisera or specific peptides reduced adhesion of oligodendroglia to astrocyte monolayers, diminished contact time between oligodendrocyte processes and individual astrocytes, and significantly increased the migration of oligodendrocyte-like cells on astrocyte monolayers. Furthermore, a soluble cadherin molecule without adhesive properties increased oligodendroglial proliferation on various extracellular matrix substrates. These data suggest that cadherins are at least partially responsible for the poor migration-promoting properties of astrocytes and that decreasing cell-cell adhesion might effect repopulation of demyelinated multiple sclerosis lesions by oligodendrocyte progenitors.     

Spinal cord histopathological alterations in a patient with longstanding complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually arises from an injury or as a complication from a surgical procedure. CRPS can result from multiple mechanisms including active processes involving both the peripheral and the central nervous system and sickness like responses involving interactions between the immune and nervous systems. In animal models both peripheral and central sensitization as well as loss of inhibition has been implicated in neuropathic pain states. Glial cells, in particular microglia and astrocytes, are the immunocompetent cells in the central nervous system and are activated following tissue injury or inflammation. In animal studies, activated glia have been shown to be both necessary and sufficient for enhanced nociception. Using immunohistochemical techniques, this study evaluated the degree of astrocytic and microglial activation as well as neuronal loss in autopsy tissue from the cervical, thoracic and lumbar spinal cord of a patient afflicted with CRPS as compared to four control individuals. The major findings of this study are that in long standing CRPS there was significant posterior horn cell loss and activation of both microglia and astrocytes most prominently at the level of the original injury but extending throughout the entire length of the spinal cord. Our hope is that the data obtained from this and other studies of autopsy material may aid in elucidating the mechanisms involved in the pathophysiology of CRPS, which may lead to the refinement of current therapies as well as novel treatments.     

Chemotaxis and accumulation of nerve growth factor by microglia and macrophages

Astrocytes and microglia play a critical role in the reaction of the central nervous system (CNS) to trauma. Although both astrocytes and microglia can produce it, accumulation of immunoreactive nerve growth factor (the prototype neurotrophin important for the survival of several classes of neurons) was observed selectively in cultured microglia and macrophages, rather than in astrocytes. Furthermore, microglia were found to display chemotaxis toward a localized source of nerve growth factor and, as demonstrated by autoradiography, take up extracellular nerve growth factor. These findings suggest that microglia, the brain's own macrophages, participate in the regulation of nerve growth factor availability in a site-specific manner. This novel function may assume a general importance both in the CNS and the peripheral nervous system at critical times after trauma when this neurotrophin is needed for nerve cell survival. © 1995 Wiley-Liss, Inc.     

Delayed wallerian degeneration in the central nervous system of Ola mice: an ultrastructural study.

The ultrastructural features of wallerian degeneration in the optic nerves of the mutant mouse, C57BL/Ola, was compared with that occurring in age matched control mice, to determine whether the previously described defect in the peripheral nervous system was present in the central nervous system as well. On ultrastructural examination, marked delay in the rate of degeneration was seen in the Ola mice nerves seen most clearly at all stages up to 4 weeks post-enucleation, following which differences progressively became undetectable. Once degeneration began, however, the pattern and mechanisms were similar to those seen in control animals, with macrophages, oligodendrocytes, and astrocytes apparently behaving similarly. In both the experimental animals and the controls, the rate of degeneration was slower than that seen in the peripheral nervous system. This study confirms a previous electrophysiological study that the defect in this mutant affects axons in both the peripheral and the central nervous systems.     

Contact-spacing among astrocytes is independent of neighbouring structures: In vivo and in vitro evidence

We have examined the morphology of astrocytes and the arrays they form in two situations, in retinas from which ganglion cells and blood vessels have been caused to degenerate, and in vitro. These observations were made to test whether the regularity of the spacing of astrocytes within normal central nervous tissue results from interaction among astrocytes, or from interaction between astrocytes and other elements of that tissue. Both in the partially degenerated cat retina, and in cultures of astrocytes from neonatal rat cortex, astrocytes make and maintain contact with neighbouring astrocytes, yet space their somas apart, giving regularity to the arrays. These results support the hypothesis that the regularity observed in arrays of astrocytes in intact tissue results from an interaction among astrocytes, independent of neighbouring structures, and lead us to suggest that the cell-cell interactions involved in contact spacing serve to distribute astrocytes through the central nervous system, and may, in other tissues, underlie the formation of epithelia. © Wiley-Liss, Inc.     

Effect of C-type natriuretic peptide (CNP) on water channel aquaporin-4 (AQP4) expression in cultured astrocytes

Astrocytes play a vital role in volume and ion control in the central nervous system. C-type natriuretic peptide (CNP) may be involved in neuronal-glial signaling, but its physiological role has not yet been characterized. In our study, we found that CNP can regulate the water channel aquaporin-4 (AQP4) expression in cultured astrocytes. Using immunocytochemistry and enzyme immunoassay, we found that primary neuronal cultures exhibited a high level of reactivity to CNP, and that cultured astrocytes exhibited reactivity to cyclic GMP after exposure of CNP. Using RT-PCR, immunoblot and immunocytochemistry, we detected increased levels of AQP4 mRNA and AQP4 immunoreactivity in the cultured astrocytes after they had been exposed to CNP or cyclic GMP. These results suggest that CNP, which is mainly produced by the neurons, effects the level of AQP4 in the astrocytes. Therefore, CNP may be a regulator of water homeostasis in the central nervous system.