Chemokines and Cytokines Required for Migration of Mesechymal Stem Cells into Marrow or Injured Tissues.

Background: Intravenous infusion of mesenchymal stem cells (MSC) after chemotherapy are currently used to accelerate the hematopoietic recovery but their potential of migration and homing to bone marrow is poorly understood.

Methods: Bone marrow MSC (BM-MSC) were isolated with the classical plastic adhesion method. Cultured MSC were identified through their expression of SH2, SH3, CD44, CD105 but lacked typical hematopoietic antigens: CD14, CD31, CD34, CD45 and CD62-e. The MSC migration was evaluated using matrigel invasion chamber assay. MSC were used at 5.10⁵ cells/mL in the upper chamber. In the bottom chamber, different cytokines were tested for their chemoattractive properties: SDF-1 (100ng/mL), PDGF-bb (100ng/mL), IGF (0,5 μg/mL) and IL-6 (100ng/mL) in a serum free medium. BM-MSC conditionned medium (CM) at 10% was also used as chemoattractant. After 24 hours, cells that had not migrated were removed from the top of the insert by scrubbing with a cotton swab and cells that migrated through the membrane were counted after staining with 0,5% crystal violet.

Results: We observed that MSC migration was greater in the presence of PDGF-bb, IL-6 or with 10% CM with respectively an increase of 6,6; 5,6 and 5 fold compared to spontaneous migration. Only a small number of MSC migrated in response to SDF-1, and this observation correlates with the very low expression of CXCR4 receptor (0,67±0,08%). Indeed, we demonstrated that CXCR4, the SDF-1 receptor was mainly intracytoplasmic expressed (74,9±1,3%).

Conclusions: IL-6 and PDGF-bb are important cytokines produced by the bone marrow microenvironment or by injured tissues. In our study, we thus demonstrated that these chmokines could be involved in the migration of MSC to bone marrow as well as to damaged tissues.