Isolation and perivascular localization of mesenchymal stem cells from mouse brain

Background: Although originally isolated from the bone marrow, mesenchymal stem cells (MSCs) have recently been detected in other tissues. However, little is known about MSCs in the brain. Objective: To determine the extent to which cells with the features of MSCs exist in normal brain tissue and to determine the location of these cells in the brain. Methods: Single-cell suspensions from mouse brains were cultured according to the same methods used for culturing bone marrow-derived MSCs (BM-MSCs). These brain-derived cells were analyzed by fluorescence-activated cell sorting for surface markers associated with BM-MSCs (stem cell antigen 1 [Sca-1], CD9, CD45, CD11b, and CD31). Brain-derived cells were exposed to mesenchymal differentiation conditions. To determine the locations of these cells within the brain, sections of normal brains were analyzed by immunostaining for Sca-1, CD31, and nerve/glial antigen 2. Results: Cells morphologically similar to mouse BM-MSCs were identified and called brain-derived MSCs (Br-MSCs). Fluorescence-activated cell sorting indicated that the isolated cells had a surface marker profile similar to BM-MSCs, ie, Sca-1, CD9, CD45, and CD11b. Like BM-MSCs, Br-MSCs were capable of differentiation into adipocytes, osteocytes, and chondrocytes. Immunostaining indicated that Sca-1 Br-MSCs are located around blood vessels and may represent progenitor cells that serve as a source of mesenchymal elements (eg, pericytes) within the brain. Conclusion: Our results indicate that cells similar to BM-MSCs exist in the brain. These Br-MSCs appear to be located within the vascular niche and may provide the mesenchymal elements of this niche. Because MSCs may be part of the cellular response to tissue injury, Br-MSCs may represent targets in the therapy of pathological processes such as stroke, trauma, and tumorigenesis.