A side order of stem cells: The SP phenotype

A defining property of murine hematopoietic stein cells (HSCs) is low fluorescence after staining with Hoechst 33342 and Rhodamine 123. These dyes have proven to be remarkably powerful tools in the purification and characterization of HSCs when used alone or in combination with antibodies directed against stem cell epitopes. Hoechst low cells are described as side population (SP) cells by virtue of their typical profiles in Hoechst red versus Hoechst blue bivariate fluorescent-activated cell sorting dot plots. Recently, excitement has been generated by the findings that putative stem cells from solid tissues may also possess this SP phenotype. SP cells have now been isolated from a wide variety of mammalian tissues based on this same dye efflux phenomenon, and in many cases this cell population has been shown to contain apparently multipotent stem cells. What is yet to be clearly addressed is whether cell fusion accounts for this perceived SP multipotency. Indeed, if low fluorescence after Hoechst staining is a phenotype shared by hematopoietic and organ-specific stem cells, do all resident tissue SP cells have bone marrow origins or might the SP phenotype be a property common to all stem cells? Subject to further analysis, the SP phenotype may prove invaluable for the initial isolation of resident tissue stem cells in the absence of definitive cell-surface markers and may have broad-ranging applications in stem cell biology, from the purification of novel stem cell populations to the development of autologous stem cell therapies.

Brain tumour stem cells

The dogma that the genesis of new cells is a negligible event in the adult mammalian brain has long influenced our perception and understanding of the origin and development of CNS tumours. The discovery that new neurons and glia are produced throughout life from neural stem cells provides new possibilities for the candidate cells of origin of CNS neoplasias. The emerging hypothesis is that alterations in the cellular and genetic mechanisms that control adult neurogenesis might contribute to brain tumorigenesis, thereby allowing the identification of new therapeutic strategies.

Transplantation of mesenchymal stem cells promotes an alternative pathway of macrophage activation and functional recovery after spinal cord injury

Abstract Mesenchymal stem cells (MSC) derived from bone marrow can potentially reduce the acute inflammatory response in spinal cord injury (SCI) and thus promote functional recovery. However, the precise mechanisms through which transplanted MSC attenuate inflammation after SCI are still unclear. The present study was designed to investigate the effects of MSC transplantation with a special focus on their effect on macrophage activation after SCI. Rats were subjected to T9-T10 SCI by contusion, then treated 3 days later with transplantation of 1.0×10(6) PKH26-labeled MSC into the contusion epicenter. The transplanted MSC migrated within the injured spinal cord without differentiating into glial or neuronal elements. MSC transplantation was associated with marked changes in the SCI environment, with significant increases in IL-4 and IL-13 levels, and reductions in TNF-a and IL-6 levels. This was associated simultaneously with increased numbers of alternatively activated macrophages (M2 phenotype: arginase-1- or CD206-positive), and decreased numbers of classically activated macrophages (M1 phenotype: iNOS- or CD16/32-positive). These changes were associated with functional locomotion recovery in the MSC-transplanted group, which correlated with preserved axons, less scar tissue formation, and increased myelin sparing. Our results suggested that acute transplantation of MSC after SCI modified the inflammatory environment by shifting the macrophage phenotype from M1 to M2, and that this may reduce the effects of the inhibitory scar tissue in the subacute/chronic phase after injury to provide a permissive environment for axonal extension and functional recovery.

Microspheres as a vehicle for biomolecule delivery to neural stem cells

Neural stem cells (NSC) are a valuable model system for understanding the intrinsic and extrinsic controls for self-renewal and differentiation choice. They also offer a platform for drug screening and neurotoxicity studies, and hold promise for cell replacement therapies for the treatment of neurodegenerative diseases. Fully exploiting the potential of this experimental tool often requires the manipulation of intrinsic cues of interest using transfection methods, to which NSC are relatively resistant. In this paper, we show that mouse and human NSC readily take up polystyrene-based microspheres which can be loaded with a range of chemical or biological cargoes. This uptake can take place in the undifferentiated stage without affecting NSC proliferation and their capacity to give rise to neurons and glia. We demonstrate that ß-galactosidase-loaded microspheres could be efficiently introduced into NSC with no apparent toxic effect, thus providing proof-of-concept for the use of microspheres as an alternative biomolecule delivery system.