ISSN:0894-1491    

DOI:10.1002/glia.440060302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo plasminogen activators (PAs): tissue‐type plasminogen activator (t‐PA) and urokinase‐type plasminogen activator (u‐PA), as well as the type‐1 plasminogen activator inhibitor (PAI‐1) are synthesized and secreted by rat astrocytes. Preliminary studies suggest that PA activity plays a role in astrocyte development and differentiation. We have examined the regulation of the PA system by the cAMP‐dependent protein kinase (PKA) and protein kinase C (PKC) in purified rat astrocyte cultures. PKA activity was increased by exposing cultured astrocytes to forskolin or dibutyryl cyclic AMP, whereas PKC activity was stimulated with phorbol‐12‐myristate 13‐acetate (PMA). Activation of both second‐messenger pathways produced a time‐ and dose‐dependent increase in the total PA activity. However, based on SDS‐PAGE/zymography we found that forskolin increased t‐PA activity and reduced u‐PA activity, whereas PMA treatment caused a significant increase in u‐PA activity without altering t‐PA activity. Reverse zymography analysis revealed that astrocyte PAI‐1 activity is decreased by forskolin and increased by PMA. Together, these results demonstrate that the components of the PA system in rat astrocytes are independently and reciprocally regulated by PKA and PKC. Our findings raise the possibility that the plasminogen activator system could be involved in some of the actions of growth factors and/or neuromodulators that modulate PKC or PKA

ISSN:0894-1491    

DOI:10.1002/glia.440060303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study was performed in order to follow the response of rat cerebellum astroglial cells (Bergmann glial cells and astrocytes) to long‐term portacaval shunt (PCS), by means of glial fibrillary acidic protein (GFAP) and vimentin immunoreactivities. Bergmann glia accumulated GFAP in response to PCS, whereas astrocytes decreased GFAP immunoreactivity when compared to control rats. The increase of GFAP occurs in cells located in the cerebellar layer where glutamate is mainly released. Since the vimentin content remained unaltered in response to PCS, when compared to control rats, it can be concluded that only the GFAP filaments are affected by PCS. Nevertheless, GFAP immunoreactivity presents regional differences in the cerebellar astroglial population, and the factors responsible for these variations are still unknown. © 1992 Wiley‐Liss,

ISSN:0894-1491    

DOI:10.1002/glia.440060304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have previously shown that in hypothalamic mixed neuronal‐glial cultures both astrocytic shape and distribution of glial fibrillary acidic protein (GFAP) are modified by estradiol. In the present study, we have investigated whether or not the presence of neurons is necessary for these hormonal effects. In mixed neuronal‐glial hypothalamic cultures the proportion of process‐bearing GFAP‐immunoreactive cells was significantly increased after treatment for 30 min with 10−12M 17β estradiol. This effect was present for at least 1 day and was reverted by incubating the cells in estradiol‐free medium. Estradiol incubation resulted in a progressive differentiation of GFAP‐immunoreactive cells from a flattened epithelioid morphology to bipolar, radial, and stellate shapes. This effect was not observed in pure hypothalamic glial cultures. Furthermore, incubation of hypothalamic glial cells with medium conditioned by estradiol‐treated mixed hypothalamic cultures did not affect the shape of GFAP‐immunoreactive astrocytes. In contrast, addition of hypothalamic neurons, but not cerebellar neurons or fibroblasts, to established hypothalamic glial cultures affected the development of estradiol sensitivity in astrocytes. These results indicate that estradiol induction of shape changes in hypothalamic astrocytes is not only dependent on the presence of hypothalamic neurons, but that physical contact between astrocytes and neurons is necessary for the manifestation of the effect of this hormone. © 1

ISSN:0894-1491    

DOI:10.1002/glia.440060305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractProtein kinase C (PKC), an enzyme involved in signal transduction, responds to diacyl glycerol and also to phorbol ester, a ligand analogous to diacyl glycerol. We have studied the expression of the major isoforms (α, βI, βII, and γ) in eight human glioblastoma cell lines. In all eight lines, PKC‐α mRNA and protein were expressed. In none of the eight did a probe for PKC‐βI and ‐βII mRNA give positive results nor were Western blots for PKC‐βII positive. The half‐life for PKC α mRNA was approximately 16 h and levels of the mRNA were increased slightly following addition of phorbol myristate acetate (PMA) or transforming growth factor‐beta (TGFβ). PKC‐γ was present in most of the glioblastomas. In cell line A172, 82% of the PKC‐α was present in the cytosol with the remainder evenly divided between plasma membrane and nucleus. Thirty minutes after addition of PMA, 33% of the total original protein was in the plasma membrane and 48% in the nuclear fraction. By 21 h, no PKC‐α was recovered from any fraction. PKC‐γ was also down‐regulated in the presence of PMA, but there was no evidence for translocation to the plasma membrane or nuclear fraction. In a more detailed study, translocation of PKC‐α in the presence of PMA was complete by 10 min, and a major decrease in the PKC translocated to the plasma‐membrane fraction occurred some time between 2 and 4 h after PMA addition, while a major decrease in the translocated nuclear fraction occurred some time after 6 h. cAMP alone had no effect on the PKC α protein level or distribution, nor did it alter the translocation and down‐regulation due to PMA exposure. In these studies the level of PKC‐α mRNA in tumors was similar to that

ISSN:0894-1491    

DOI:10.1002/glia.440060306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractZinc is a potent inducer of the 72 kD heat shock protein (HSP72). In brain, pathological conditions such as ischemia and seizures increase extracellular zinc. The present study examines the effect of zinc on HSP72 expression in rat primary cortical astrocyte culture. Astrocytes were grown to confluence and exposed to zinc chloride in CO2‐equilibrated Earle's buffered salt solution. Expression of HSP72 was examined using immunocytochemistry. HSP72 was induced with zinc concentrations of 5 to 100 μM after 4 h exposures, or 200 to 300 μM after 15 min exposures. At the lower concentrations expression occurred in small clusters of contiguous cells. At concentrations high enough to cause cell death, HSP72‐positive astrocytes formed a continuous margin around patches of dead cells. These patterns of HSP72 expression are similar to the patterns seen after cerebral ischemia in vivo. Exposure to zinc at 100 μM for 4 h or 400 μM for 15 min caused greater than 90% cell death. Increases in extracellular zinc may contribute to HSP72 induction and astrocyte death under ischemia and other pathological conditions in brain. © 1992 Wiley

ISSN:0894-1491    

DOI:10.1002/glia.440060307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractGlial cells execute essential functions in central nervous system (CNS) development and are also believed to play important roles during gliosis in response to trauma or disease. These developmental and pathological states have also been associated with elevated expression of opioid genes. Because levels of the cytokine interleukin‐1β (IL‐1β) increase following CNS lesions, we examined the possible influence of IL‐1β on the expression of opioid genes in astrocytes cultured from rat cortex. Proenkephalin mRNA expression was stimulated by IL‐1β in a time‐ and concentration‐dependent manner, being maximal with 5 U/ml IL‐1β at 4h. Although the β‐adrenergic agonist isoproternol was also active, interferon, glutamate, and carbacol were not. Unlike isoproterenol, the actions of IL‐1β were not associated with a cyclic adenosine monophosphate (AMP)‐dependent pathway. Interleukin‐1β also regulated a proenkephalin‐chloramphenicol acetyltransferase fusion gene transiently transfected into astrocytes, with a dose‐response similar to that active in proenkephalin mRNA. These effects of IL‐1β were region‐specific, not being observed with either cerebellar or hippocampal astrocytes; however, isoproterenol was active in the latter cell populations. Proenkephalin mRNA in cortical astrocytes was stimulated following a temperature stress. These results suggest that enhanced proenkephalin gene expression in astrocytes by IL‐1β may be important in neuroimmune interactions and in trauma‐induced C

ISSN:0894-1491    

DOI:10.1002/glia.440060308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractHeterogeneity among astrocytes suggests that their role in the central nervous system is more complex than is commonly recognized. This paper describes just such a functional difference, comparing gap junctions in astrocytes derived from two brain regions. Astrocytes, both in situ and in culture, employ gap junctions as a means of intercellular communication. Recent evidence utilizing cultured rat cortical and striatal astrocytes has shown that these channels consist of subunits of connexin 43, the same protein as that composing cardiac gap junctions. Here we report that astrocytes cultured from neonatal rat hypothalamus contain a greater number of functional channels than astrocytes from the striatum, a difference reflected in both connexin 43 protein and mRNA. Specifically, in hypothalamic astrocytes the level of connexin 43 protein was approximately four times that found in comparable cultures from the striatum, as determined by immunoblotting. Complementary results from immunocytochemical experiments using an antibody specific for connexin 43 reveal significantly greater fluorescence in astrocytes cultured from the hypothalamus as compared to those from the striatum. Northern blot analysis showed that connexin 43 mRNA levels were also approximately 4‐fold greater in the hypothalamic cultures, consistent with difference seen by immunoblotting. Finally, dye coupling studies using confluent cultures consistently showed that within 1 min Lucifer Yellow injected into striatal astrocytes spread to immediately surrounding cells while in hypothalamic astrocytes dye often spread to apparent third or fourth order neighbors within the same time period. Thus, the higher level of connexin 43 expression seen in hypothalamic astrocytes results in cells with greater numbers of functional channels. Interestingly, both the immunocytochemical and dye coupling experiments also revealed heterogeneity, among cells derived from each brain area, indicating that both region contain subpopulations of astrocytes. Taken together, our data show differences in gap junction expression, both within and between astrocytes derived from two brain regions. Further, this heterogeneity appears to derive from differences in either transcriptional regulation or in mRNA stability, and not from changes in the relative levels of phosphorylated forms of connexin 43. Thus, these data, which are consistent with light microscopic immunocytochemical studies in tissue sections of rat brain, predict that, in vivo, region‐specific coupling subserves functional specialization within the central nervous system. © 1992 Wiley‐Lis

ISSN:0894-1491    

DOI:10.1002/glia.440060309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe cellular skeleton of the adult rat fimbria consists of regularly spacedinterfascicular glial rowsof considerable length, running in the longitudinal (axonal) axis of the tract.Each row consists of a series of repeatedsegmentsmade up of a stretch of interfascicular oligodendrocytes lying in direct contact with each other, and separated from the adjacent segments by usually solitary interfascicular astrocytes. A typical segment would be around 60 μm long, and have an axial core of about eight contiguous oligodendrocytes surrounded by a shell of about 1,200 axons, 70% of which are myelinated. In the transverse plane of the tract, adjacent segments are stacked together with a core‐to‐core distance of around 15 μm.The interfascicular oligodendrocytes haveradial stem processes(in a plane transverse to the axonal axis) which give rise to thelongitudinal myelinating (internodal) processes. Both transverse and longitudinal oligodendrocytic processes are longer than the dimensions of the segment (in which their cell bodies lie) and its axonal shell. They thus cooperate in myelinating axons of adjacent segments in both planes.The interfascicular astrocytes have three distinct types of processes: radial, longitudinal, and vascular (bearing end feet). Theradial astrocytic processesare thick and tapering, and the processes of individual astrocytes extend transversely (in the plane of the original embryonic radial glial processes) for a total of at least 100 μm. The considerably more numerouslongitudinal astrocytic processesarise from all parts of the cell bodies and radial processes. They are up to at least 30 μm long, thin, untapering, and largely unbranched, and are interdigitated among the fimbrial axons.In the radial plane, the astrocytic radial processes spread out through a wide swathe of adjacent segments, so that the integrated meshwork of interpenetrating longitudinal processes arising from overlapping radial processes of astrocytes from many different interfascicular rows provides a continuous longitudinal substrate for the fimbrial axons. © 1992 Wiley

ISSN:0894-1491    

DOI:10.1002/glia.440060310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA glycoprotein that induces γ‐aminobutyric acid (GABA) carriers in cultured cerebellar astrocytes was isolated and purified from conditioned media from cultured cerebellar granule cells by anion exchange chromatography, affinity chromatography, and gel filtration. Following gel filtration three fractions corresponding to Mr30,000, 60,000, and 240,000 exhibited GABA carrier inducing activity. SDS‐PAGE of the Mr30,000 fraction revealed under non‐reducing conditions three bands corresponding to Mr30,000, 60,000, and 120,000. Under reducing conditions only the band corresponding to an Mrof 30,000 was visible. An identical N‐terminal amino acid sequence and amino acid composition was found in the Mr30,000 and the Mr60,000 fraction from the gel filtration. These results suggest that the protein polymerizes into di‐ and tetramers. Computer base analysis of the N‐terminal amino acid sequence revealed no obvious homology with previously reported N‐terminal amino acid sequences.Application of the glycoprotein to cerebellar astrocytes led time and dose dependently to an increased GABA uptake. The effect became maximal after 24h exposure of the cells. Kinetic analysis of the GABA uptake showed that exposure of the astrocytes to the glycoprotein led to an increase in Vmaxfor GABA uptake without affecting Km, suggesting an increase in the number of GABA carrier molecules. Addition of actinomycin D together with the glycoprotein abolished this effect suggesting that the glycoprotein acts by stimulating de novo synthesis of GABA carriers. Hence, the newly purified protein secreted from neurons is named GABA‐carrier inducing protein (GABA‐CIP). © 1

ISSN:0894-1491    

DOI:10.1002/glia.440060311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY