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M Mallat

Publications and source records attributed to M Mallat.

At least 19 recordsLinked to original sources
PubMed1998

Identification of CSF-1 as a brain macrophage migratory activity produced by astrocytes.

Intraparenchymal migration of macrophages occurs in the CNS during development or as a consequence of tissue injuries. In the present study, we have shown, by using an in vitro chemotaxis assay, that cultured rat astrocytes obtained from the developing cerebral cortex and striatum produce soluble factors, which attract purified brain macrophages. The effect of astrocyte-derived factors on macrophages was strongly reduced in the presence of antibodies neutralizing colony-stimulating factor 1 (CSF-1, also called M-CSF), and recombinant CSF-1 was found to act as a chemotactic agent on brain macrophages. Synthesis of CSF-1 by cultured astrocytes was confirmed by northern detection of CSF-1 transcripts. In contrast, the CSF-1 gene was not expressed by cultured neurons from the cerebral cortex and striatum or by the brain macrophage population responsive to CSF-1 gradient. ELISA detection of CSF-1 in tissue extracts revealed the occurrence of this cytokine in the rat cerebral cortex during postnatal development and in adults. Altogether, our results demonstrate that astrocytes, through CSF-1 secretion, can trigger the polarized migration of brain macrophages and suggest a new mechanism which could regulate the locomotion of these cells in the cerebral cortex during ontogenesis or following lesions.

Animals↗
PubMed1997

Neurons promote macrophage proliferation by producing transforming growth factor-beta2.

The infiltration of bone marrow-derived macrophages into the CNS contributes to growth and reactions of microglia during development or after brain injury. The proliferation of microglial cells is stimulated by colony-stimulating factor 1 (CSF-1), an astrocyte-produced growth factor that acts on mononuclear phagocytes. In the present study, we have shown, using an in vitro model system, that rodent neurons obtained from the developing cerebral cortex produce a soluble factor that strongly enhances the proliferation of macrophages cultured in the presence of CSF-1. Both macrophages isolated from the developing brain and those from the adult bone marrow were stimulated. Kinetic analyses of [3H]thymidine incorporation into macrophages indicated that their response to the neuron-derived factor involved a shortening of the cycle of proliferating cells. The effect of neurons on macrophages was blocked in the presence of antibodies neutralizing transforming growth factor-beta2 (TGF-beta2), whereas recombinant TGF-beta2 stimulated macrophage proliferation in the presence of CSF-1. Neuronal secretion of TGF-beta2 was confirmed by reverse transcription-PCR detection of TGF-beta2 transcripts and immunodetection of the protein within neurons and in their culture medium. In situ hybridization and immunohistochemical experiments showed neuronal expression of TGF-beta2 in sections of cerebral cortex obtained from 6-d-old rats, an age at which extensive developmental recruitment of macrophages occurs in this cerebral region. Altogether, our results provide direct evidence that neurons have the capacity to promote brain macrophage proliferation and demonstrate the role of TGF-beta2 in this neuronal function.

Animals↗
PubMed1996

Production of monocyte chemotactic protein-1 by rat brain macrophages.

In the present study, we show that cultured rat brain macrophages release a soluble factor that stimulates the migration of bone marrow-derived macrophages, as determined by an in vitro chemotaxis assay. A checkerboard analysis indicated that most of this effect resulted from a polarized migration of the cells (chemotactic phenomenon), rather than in an increase in cell motility (chemokinesis). This activity was significantly decreased by an immune serum directed against the rat monocyte chemoattractant protein-1 (chemokine MCP-1). Northern blot analysis demonstrated expression of the MCP-1 gene in cultured brain macrophages, but its absence in unstimulated bone marrow-derived macrophages. Up-regulation of MCP-1 expression was observed when lipopolysaccharide was added to cultured brain macrophages, a peak occurring after a 6 h period of stimulation. Also, inflammatory cytokines such as interleukin (IL)-1 beta, colony stimulating factor-1, tumour necrosis factor-alpha and IL-6 individually increased the basal level of MCP-1 mRNA. Subsequently, we demonstrated the in vivo production of MCP-1 in the adult rat brain following injury induced by a local injection of kainic acid. MCP-1 synthesis was localized in both astrocytes and brain macrophages. These results suggest that the activation of resting microglial cells into brain macrophages and their subsequent secretion of chemokines could contribute to the mechanism(s), leading to the infiltration of the CNS by blood-derived monocytes, as observed in several pathologies.

Animals↗
PubMed1996

Recruitment of brain macrophages: roles of cytokines and extracellular matrix proteins produced by glial or neuronal cells.

Brain macrophages are a subpopulation of microglial cells which occur in the developing or in the injured CNS. These cells actively contribute to CNS tissue remodeling by acting on neuronal and macroglial lineages. Recruitment of brain macrophages is promoted by transformation of resting microglial phenotypes, infiltration of the tissue by exogenous macrophage precursors and local proliferation of phagocytes. These events are regulated by extracellular signals produced by glial cells or neurons. Studies based on in vitro cell cultures or experimental tissue lesions suggest that the infiltration of phagocytes involves intracerebral production of chemotactic factors acting on monocytes such as chemokines or extracellular matrix proteins. Proliferation of brain macrophages in stimulated by colony-stimulating factors which seem to be primarily secreted by glial cells.

Astrocytes↗
PubMed1995

Immunohistochemical detection of thrombospondin in microglia in the developing rat brain.

The development of microglia involves the expression of a phenotype displaying phagocytic behaviour termed brain macrophage or amoeboid microglial cell. We have previously shown that rat brain macrophages purified in vitro secrete thrombospondin, an extracellular matrix protein, which acts on cultured neuronal cells by promoting neurite growth. In the present study, the expression of thrombospondin was investigated in tissue sections of the developing rat forebrain in relation to the distribution of microglia. These cells were identified using anti-macrophage antibodies and the isolectin B4 from Bandeiraea simplicifolia. Immunocytochemical detection of thrombospondin clearly outlined a cell population displaying the morphologies and distribution of brain macrophages, from the 17th day of embryonic life up to the end of the second postnatal week. These cells were most numerous in cortical and subcortical regions of developing fibre tracts such as the corpus callosum or the internal capsule. The localization of thrombospondin in brain macrophages was confirmed by double immunostaining using ED1 monoclonal anti-macrophage antibodies. Ramified microglial cells were also labelled transiently by anti-thrombospondin antibodies during early postnatal life. These results provide in situ evidence supporting the notion that microglial cells could favour axonal growth by producing thrombospondin during development.

Aging↗
PubMed1994

Brain macrophages stimulate neurite growth and regeneration by secreting thrombospondin.

The presence of macrophages in the developing or lesioned central nervous system (CNS) led us to study the influence of these cells on neuronal growth. Macrophages were isolated from embryonic rat brain and we observed that factors released in vitro by these cells stimulate neurite growth and regeneration of cultured CNS neurons. This effect was inhibited by antibodies directed against thrombospondin, an extracellular matrix protein that we found to be synthesized and released by brain macrophages. Immunodetection of thrombospondin in the adult rat brain lesioned by kainic acid confirmed the production of this protein by brain macrophages and indicated an early intraparenchymal accumulation of thrombospondin following injury. These results suggest that brain macrophages contribute actively to neurite growth or regeneration during the development or in pathological contexts.

Animals↗
PubMed1994

Downregulation of in vitro neurotoxicity of brain macrophages by prostaglandin E2 and a beta-adrenergic agonist.

Brain macrophages (BM), a subpopulation of microglia, have the ability to kill neurons by producing reactive oxygen intermediates. Cocultures of neurons and macrophages derived from the cerebral cortex of rat embryos were used to look for regulation of BM neurotoxicity. Isoproterenol (10(-7) M), a beta-adrenergic agonist, induced a significant inhibition of BM neurotoxicity and this effect was abolished in the presence of propranolol, a beta-adrenergic antagonist. BM neurotoxicity was also reduced in the presence of prostaglandin E2 (10(-8), 10(-6) M), a metabolite derived from arachidonic acid. These results suggest endogenous mechanisms of neuroprotection operating either during development or following lesions.

Adrenergic beta-Agonists↗
PubMed1994

Brain macrophages: neurotoxic or neurotrophic effector cells?

The development of the central nervous system and various pathological contexts imply remodeling or alteration of neuronal networks associated with tissue recruitment of mononuclear phagocytes. Purification and culture of brain macrophages have provided a tool for investigating the functions of these cells. We discuss different mechanisms whereby macrophages could directly influence the survival of neurons and the growth of their processes.

Brain↗
PubMed1993

Influence of interleukin-1 and tumor necrosis factor alpha on the growth of microglial cells in primary cultures of mouse cerebral cortex: involvement of colony-stimulating factor 1.

The influence of monokines and CNS-derived colony-stimulating factors (CSF) on the growth of microglia has been studied in mixed glial primary cultures stemming from mouse embryos. We observed that spontaneous growth of microglial cells in the presence of astrocytes is blocked by adding anti-colony-stimulating factor 1 (CSF-1) antibodies to the cultures. Both interleukin-1 (IL-1) and tumor necrosis factor-alpha(TNF alpha) strongly increased the number of microglial cells in mixed glial cultures and this effect was prevented by anti-CSF-1 antibodies. In contrast, anti-interleukin-3 (IL-3) or anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibodies did not significantly affect the in vitro growth of microglia. These results provide functional significance to astrocytic productions of CSF-1 and their modulations by IL-1 or TNF alpha.

Animals↗
PubMed1992

Interleukin 1 and tumor necrosis factor-alpha stimulate the production of colony-stimulating factor 1 by murine astrocytes.

Astrocytes have the ability to secrete colony-stimulating factor 1 (CSF-1), a growth factor known to stimulate the proliferation of brain macrophages. We have studied the effect of cytokines such as interleukin 1 (IL-1), tumor necrosis factor-alpha (TNF alpha), and interleukin 6 (IL-6) on the production of CSF-1 by cultured primary astrocytes and an astrocytic cell line derived from embryonic mouse brain. We observed that both TNF alpha and IL-1 increased CSF-1 mRNA and protein levels in the astrocytic cultures. In contrast, IL-6 was ineffective. The CSF-1 mRNA levels were strongly reduced by incubating immortalized astrocytic cells with staurosporine, a protein kinase C inhibitor, both in the absence and in the presence of cytokines. Conversely, 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C activator, increased CSF-1 mRNA levels. These results suggest a mechanism whereby mononuclear phagocytes could favor their own recruitment in the CNS by producing cytokines.

Animals↗
PubMed1991

Fibronectin and laminin regulate the in vitro differentiation of microglial cells.

During development, the differentiation of ameboid microglia (brain macrophages) into ramified microglia is marked by a loss of macrophage-like properties and the extension of thin cytoplasmic projections. We have studied the influence of two extracellular matrix proteins, laminin and fibronectin, on microglia differentiation, using cell cultures. Brain macrophages were isolated from primary glial layers derived from embryonic rat brain and further cultured in serum-free medium. The addition of fibronectin induced the transformation of round or spindle-shaped brain macrophages into cells displaying a reduced cell body and extending thin and long processes. This morphological transformation was associated with a reorganization of the vimentin network, including a condensation of dispersed filaments into thick bundles and a modification of the phosphorylation state of vimentin monomers. In addition, compared to brain macrophages, the process-bearing microglia lost the ability to engulf zymosan particles, and showed reduction in non-specific esterase activity and superoxide anion generation. In contrast, laminin reduced the spontaneous transformation of brain macrophages into process-bearing cells. Moreover, laminin and serum induced a reverse transformation of process-bearing cells when added to cultures pretreated with fibronectin. Altogether these results demonstrate antagonist effects of fibronectin and laminin on the in vitro differentiation of brain macrophages towards a "resting" phenotype, which shares several properties with the ramified microglia present in the adult brain. We suggest that fibronectin and laminin regulate the differentiation of microglial cells, which takes place during development or following various types of lesions in the adult brain.

Animals↗
PubMed1990

Expression of macrophage colony-stimulating factor gene in the mouse brain during development.

We have investigated the expression of macrophage-colony stimulating factor (M-CSF) gene in mouse brain during development. Northern blot analysis of cerebral RNA evidenced a 4.5-kb M-CSF transcript from day 14 of gestation until 2 weeks after birth. The cell type responsible for this transcription was studied using in vitro cell cultures. The 4.5-kb M-CSF transcript was found both in astrocyte primary cultures and in immortalized astrocytic cell lines. M-CSF mRNA was also detected in lipopolysaccharide-stimulated brain macrophage cultures. These results suggest that M-CSF is involved in the outgrowth of microglia during ontogenesis.

Animals↗
PubMed1989

Lineage relationship between oligodendrocytes and brain macrophages?

Cells which adhere rapidly in vitro were purified from embryonic rat brain and characterized as macrophages. These characterizations rely on (1) phagocytic behaviour, (2) non-specific esterase activity, (3) immunocytochemical criteria such as the detection of CD4, Mac 1 and class II products of the major histocompatibility complex (MHC II). Morphological transformations observed in the cultures and labeling with anti-galactocerebroside (GalC) antibodies suggest a possible transition between brain-macrophagic and oligodendrocytic phenotypes.

Animals↗
PubMed1989

Secretion of nerve growth factor in cultures of glial cells and neurons derived from different regions of the mouse brain.

The regional ability of central neurons and glial cells to produce nerve growth factor (NGF) was studied in vitro. NGF secretion was compared in cultures of perinatal astrocytes or embryonic neurons that were derived from various mouse brain structures. No regional differences were detected among cultures of post-natal day 2 glial cells of hippocampal, cortical, striatal, or mesencephalic origin. In all cases, levels of NGF released by the cells were very similar. They were closely correlated to the growth rate as shown by the fact that exponentially growing cells produced relatively more factor than did confluent cells, a finding in agreement with previous observations. Unlike growth-phase cells, primary astrocytes immediately plated at high cell density did not secrete any assayable factor before the 7th day of culture. Levels of NGF found during the following days remained low. In contrast, striking differences were observed among cultures of embryonic neurons. NGF was found in relatively large amounts in cultures of embryonic day 17 or 19 striatal neurons, whereas media conditioned by neurons from the mesencephalon, cortex, or septum contained much less factor. Amounts of NGF assayed in cultures of hippocampal neurons varied with the time of sampling of this brain structure. Levels of factor were significantly higher in media conditioned by embryonic day 19 neurons than in media of embryonic day 17 neurons. However, amounts of NGF found in supernatants of hippocampal neurons remained smaller than those present in cultures of striatal nerve cells. Altogether, the results suggest that, in addition to astrocytes, central neurons may also synthesize and secrete NGF in vitro and that this phenomenum is dependent on both the origin and the developmental stage of the neuronal population.

Animals↗
PubMed1989

Lipopolysaccharide-stimulated rat brain macrophages release NGF in vitro.

Amoeboid microglial cells purified from primary cultures of embryonic rat brains and stimulated with bacterial lipopolysaccharides released high amounts of nerve growth factor. This finding suggests that brain macrophages play a major neurotrophic role during development, in adulthood, and in the regenerative events that follow localized lesions.

Animals↗
PubMed1987

Primary cultures of murine astrocytes produce C3 and factor B, two components of the alternative pathway of complement activation.

We have investigated the production of C3, C4, and factor B complement components in primary cultures of murine astrocytes and in clonal cell lines belonging to the astrocytic lineage by immunoprecipitation of secreted labeled polypeptides. Although C4 has not been detected, C3 appeared to be constitutively synthesized both by two transformed astroblastic cell lines and by astrocytes in primary cultures. In contrast, factor B was only secreted upon lipopolysaccharide stimulation both in astroglial primary cultures and in an immortalized astrocytic cell line. The eventual physiologic relevance of an endogenous brain production of components of the alternative pathway of complement activation is discussed.

Animals↗