Purpose: CD133+CD34+ hematopoietic stem cells (HSCs) have been shown to differentiate into cell types of nonhematopoietic lineage. It is unclear whether HSCs target and repair damaged musculoskeletal tissue. We aimed to analyze if HSCs are mobilized after musculoskeletal surgery to circulation, home to surgical wound fluid (SWF)-activated endothelium, and are chemoattracted by SWF under in vitro conditions.
Methods: Circulating HSC levels were measured at t = 3, 8, 24, 48 h postoperatively using fluorescence-activated cell sorting (FACS) and compared with preoperative levels (t = 0) and normal volunteers. For adhesion experiments, HSCs were incubated on SWF-activated human umbilical vein endothelial cells (HUVECs) and HSC/HUVEC ratios determined by FACS. Adhesion receptor expression on HSC (L-selectin, lymphocyte function-associated antigen 1 (LFA-1), very late antigen-4) and SWF-activated HUVECs (P-selectin, E-selectin, V-cell adhesion molecules (CAM), I-CAM) was determined and HSC adhesion measured again after blocking upregulated receptors. Using a modified Boyden chamber, HSC chemotaxis was analyzed for an SWF and cytokine-neutralized SWF (vascular endothelial growth factor (VEGF), stromal-derived factor-1, interleukin-8) gradient.
Results: Circulating HSCs were significantly increased 8 h after surgery. Increasing HSC adhesion to HUVECs was shown for SWF isolated at any postoperative time point, and chemoattraction was significantly induced in an SWF gradient with SWF isolated 8 and 24 h postoperatively. Receptor and cytokine blockade experiments with monoclonal antibodies revealed decreased HSC adhesion to SWF-activated endothelium and showed lower chemotaxis after blocking the LFA-1-I-CAM-1 receptor axis (adhesion) and neutralizing VEGF-165 (chemotaxis).
Conclusions: Our data demonstrate that HSCs are mobilized after trauma, target to wound-associated endothelium via the LFA-1-I-CAM-1 axis, and are chemoattracted by VEGF-165 under in vitro conditions.