Abstract 192: Bone Marrow Mononuclear Cells May Enhance Recovery After Stroke By Modulating the Microglial Response

Abstract

Background: Autologous bone marrow mononuclear cells (MNCs) have been shown in multiple labs to improve stroke recovery in animal models but the mechanisms remain unclear. We assessed whether MNCs modulate macrophage-microglia responses in acute stroke. Methods: C57/BL mice were subjected to middle cerebral artery occlusion (MCAo) for 60 minutes or sham surgery. 24 hours later, they were randomized to receive saline infusion IV or 1x 10 6 autologous MNCs IV. At various time points after stroke, 1ml peripheral blood was collected and brains were harvested up to day14. Peripheral blood was labeled with anti-mouse CD45, CD115, F4/80 or Gr-1 antibodies and then assessed by flow cytometry. Microglia were isolated from brains by Optiprep gradient and stained with anti-mouse CD11b, CD45, and CD86 antibodies for evaluation by flow cytometry. For gene expression analyses by RT-PCR, microglia-macrophages were further sorted by magnetic activated-cells sorting using CD11b antibody. Results: 1) At day 2 after stroke, the percentage of CD115 + monocytes and CD115 + /Gr-1 low cells were significantly decreased in whole peripheral blood but F4/80 + macrophages were increased. MNCs increased the abundance of CD115 + /Gr-1 low cells and decreased the abundance of F4/80 + macrophages in peripheral blood compared to saline control at day 2 after stroke (n=5, p <0.05); 2)Compared to saline, MNCs significantly reduced the total number of CD11b + microglia-macrophages in the stroke-affected hemisphere at day 2 to day 6. MNCs significantly decreased the proportion of CD11b + /CD45 high among CD11b + cells at day 2 and day 4 and CD86 + cells among CD11b + cells at day 2. Among CD11b + microglia-macrophages isolated from the ipsilateral hemisphere of MNC treated mice, compared to saline treated controls, iNOS and IL-1β genes expression were down-regulated at day 2. At day 6, iNOS remained down-regulated while now IL-10, Arganase-1 and CD206 genes expression (markers for the “healing” macrophage phenotype) were up-regulated (n=3 to 5, p <0.05). Conclusions: MNCs may enhance recovery after stroke by altering monocyte trafficking and changing microglial polarization into a healing phenotype.