Abstract 4932: CXCR4 Expression on Bone Marrow-derived Cells Was Regulated Positively by Calcium and Negatively by Aging

Abstract

Cell surface receptors play major roles in the mobilization and homing of progenitor cells from the bone marrow to peripheral tissues. CXCR4 is an important receptor that regulates homing of leukocytes and vascular progenitor cells (VPC) in response to the chemokine stromal cell-derived factor-1 (SDF-1). Ionic calcium is also known to regulate chemotaxis of selective bone marrow-derived cells (BMC) through the calcium-sensing receptor CaR. We assessed the hypothesis that calcium regulates CXCR4 expression on BMC; defective CXCR4 expression develops with aging, which results in less VPC homing to vascular lesion site and inefficient repair. We found that CXCR4 surface expression is age-dependent. CXCR4 on the surface of BMC from old mice (24 months old) is significantly lower than young mice. We also found that CaCl 2 treatment of BMC from young mice induced a significant increase in both the transcription and cell surface expression of CXCR4. BMC subpopulations expressing VEGFR2 + and CD34 + , which were considered as endothelial progenitor cells, were especially sensitive to calcium. The effects were blocked by calcium influx inhibitors, anti-CaR antibody, and the protein synthesis inhibitor cycloheximide. Calcium treatment also enhanced SDF-1-mediated CXCR4 internalization. These changes were reflected in significantly improved chemotaxis by SDF-1, which was abolished by the CXCR4 antagonist AMD3100 and by antibody against CXCR4. Calcium pre-treatment improved homing of CD34 + BMC to ischemic muscle in vivo, and enhanced revascularization in ischemic mouse hindlimbs. Such calcium-mediated increase of surface CXCR4 was not observed on BMC from old mice. Pre-treatment of BMC from old mice with calcium did not significantly improve the cellular signaling response to SDF-1, nor enhance homing of injected BMC to ischemic muscle and blood reperfusion in vivo. In conclusion, we identified calcium as a positive regulator of CXCR4 expression that enhances progenitor cell mobility and efficiency of cell-based therapy. Aging negatively affects BMC CXCR4 expression and its interaction with SDF-1. This research has received full or partial funding support from the American Heart Association, Greater Southeast Affiliate (Alabama, Florida, Georgia, Louisiana, Mississippi, Puerto Rico & Tennessee).