The role of microglia in spinal cord injury (SCI) remains poorly understood and is often confused with the response of macrophages. Here, we use specific transgenic mouse lines and depleting agents to understand the response of microglia after SCI. We find that microglia are highly dynamic and proliferate extensively during the first two weeks, accumulating around the lesion. There, activated microglia position themselves at the interface between infiltrating leukocytes and astrocytes, which proliferate and form a scar in response to microglia-derived factors, such as IGF-1. Depletion of microglia after SCI causes disruption of glial scar formation, enhances parenchymal immune infiltrates, reduces neuronal and oligodendrocyte survival, and impairs locomotor recovery. Conversely, increased microglial proliferation, induced by local M-CSF delivery, reduces lesion size and enhances functional recovery. Altogether, our results identify microglia as a key cellular component of the scar that develops after SCI to protect neural tissue.

Alzheimer's disease is a major cause of dementia in humans. The appearance of cognitive decline is linked to the overproduction of a short peptide called beta-amyloid (Abeta) in both soluble and aggregate forms. Here, we show that injecting macrophage colony-stimulating factor (M-CSF) to Swedish beta-amyloid precursor protein (APP(Swe))/PS1 transgenic mice, a well-documented model for Alzheimer's disease, on a weekly basis prior to the appearance of learning and memory deficits prevented cognitive loss. M-CSF also increased the number of microglia in the parenchyma and decreased the number of Abeta deposits. Senile plaques were smaller and less dense in the brain of M-CSF-treated mice compared to littermate controls treated with vehicle solution. Interestingly, a higher ratio of microglia internalized Abeta in the brain of M-CSF-treated animals and the phagocytosed peptides were located in the late endosomes and lysosomes. Less Abeta(40) and Abeta(42) monomers were also detected in the extracellular protein enriched fractions of M-CSF-treated transgenic mice when compared with vehicle controls. Finally, treating APP(Swe)/PS1 mice that were already demonstrating installed Abeta pathology stabilized the cognitive decline. Together these results provide compelling evidence that systemic M-CSF administration is a powerful treatment to stimulate bone marrow-derived microglia, degrade Abeta and prevent or improve the cognitive decline associated with Abeta burden in a mouse model of Alzheimer's disease.

Understanding how bone marrow-derived cells (BMDCs) enter the central nervous system (CNS) is critical for the development of therapies for brain-related disorders using hematopoietic stem cells. We investigated the brain damages and blood-brain barrier (BBB) modification following either whole-body irradiation or a myeloablative chemotherapy regimen in mice, and the capacity for these treatments to induce the entry of BMDCs into the CNS. Neither treatment had a lasting effect on brain integrity and both were equally efficient at achieving myeloablation. Injection of bone marrow cells from green fluorescent protein (GFP) transgenic mice was able to completely repopulate the hematopoietic niche in the circulation and in hematopoietic organs (thymus and spleen). However, GFP + cells only entered the brain following whole-body irradiation. We conclude that myeloablation, damages to the brain integrity, or the BBB and peripheral chimerism are not responsible for the entry of BMDCs into the CNS following irradiation.Key words: Microglia; Central nervous sysem (CNS); Neuroimmunology; Hematopoietic stem cell; Irradiation; Chemotherapy; Bone marrow-derived cells; Innate immunity INTRODUCTIONof high-grade glioma, severe combined immunodeficiency, multiple sclerosis, and other CNS pathologies (6). Despite the high therapeutic potential of BMDCs for Brain-specific macrophages called microglia are responsible for the immune defense of the brain through cerebral pathologies (13) and an inestimable tool to study microglial biology, the mechanisms by which they innate immunity processes (19). They are the only brain cell type deriving from bone marrow resident hematoenter the brain are poorly understood. Chimerism is the process by which injected bone poietic stem cells (18,22). The recruitment of bone marrow-derived cells (BMDCs) into the brain is highly marrow cells from a donor take over the hematopoietic system of a recipient. The use of the green fluorescent active throughout the embryonic life during which microglia populate the central nervous system (CNS) protein heterozygous (GFP +/− ) transgenic mouse model has eased the study of chimerism by facilitating the (5). It appears to be marginal during the adult life, as self-renewal of microglia could be sufficient to maintain tracking of injected GFP + cells in a GFP − background. Numerous models have been designed to induce chimethe microglial population (1), and more active in pathological conditions such as Alzheimer's disease (8). It rism in mouse models such as parabiosis, immunosuppression of the recipient mice, and irradiation of the was demonstrated that following whole-body irradiation, bone marrow transplantation was highly efficient to whole body, only the head, or the body with a protected head (24). It appears that only lethal doses of wholerestrict amyloid plaque formation and resolve the cognitive declines of mouse models of Alzheimer's disease body irradiation are able to create an efficient chimerism and to induce migrations of BMDCs to the brain. Con-...

The properties and regulation of the mammalian polyamine transport system are still poorly understood. In estrogen-responsive ZR-75-1 human breast cancer cells, which display low polyamine biosynthetic activity, putrescine and spermidine were internalized with high affinity (Km = 3.7 and 0.5 microM, respectively) via a single class of saturable transporter shared by both substrate types, or via distinct but closely similar carriers. The Vmax, but not the Km of polyamine transport was rapidly and synergistically up-regulated by estrogens and insulin. The steady decay in transport activity observed in hormone-deprived cells was accelerated by retinoic acid. The enhancement of uptake activity resulting from polyamine depletion was amplified 3-fold by estrogens and insulin despite profound growth inhibition, indicating that the cooperative hormonal induction of polyamine transport is dissociated from cell growth status. Polyamine uptake was under feedback inhibition by at least three distinct mechanisms in these cells, namely (i) the induction of a short-lived protein not actively synthesized without ongoing uptake or upon polyamine deletion; (ii) a more latent, protein synthesis-independent "trans-inhibition" mechanism; and (iii) a post-carrier, cycloheximide-sensitive mechanism limiting substrate accumulation. The complexity of these multiple levels of feedback transport inhibition is in keeping with the cytotoxicity of excessive polyamine content.