Trafficking of human neural stem cells is regulated by stromal cell-derived factor-1α / CXC- chemokine receptor 4 signaling

Abstract

Stimulation of endogenous neural stem cells (NSCs) or NSCs transplantation via systemic or intraparenchymal injection has been reported as potentially powerful new therapeutic strategies for various neurological disorders. However, the trafficking of NSCs to areas of tissue damage is poorly understood. Stromal cell-derived factor-1 (SDF-1) and the chemokine receptor CXCR4 are highly expressed in the central nervous system, and are essential to homing of circulating hamatopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and cancer cells to bone marrow and liver. In the ischemic brains, expression of SDF-1 and CXCR4 is upregulated in the penumbral area. To extend these observations, we used human NSCs (F3) line to investigate CXCR4 and SDF-1 expression with FACS analysis to determine the intracellular distribution of CXCR4 receptors. To verify the effect of SDF-1 on human NSCs, transwell assay toward SDF-1 gradient was performed. Protective effects of SDF-1 were evaluated by spontaneous apoptosis with serum /growth factor withdrawal, cell cycle analysis with FACS, and BrdU / Ki-67 labeling index. Human NSCs express SDF-1 and CXCR4. FACS analysis showed most human NSCs had intracellular form of CXCR4 (98-99%), while 0.5-4% of them express in the membrane surface. CXCR4 protein was present in two forms, 49 kDa and 82 kDa (N-glycosylated form), similar to the patterns in MSCs (dimeric, 66/130 kDa) but different from those of HSCs or cancer cells. SDF-1 (5 ng/ml) inhibited 54 % of spontaneous apoptosis induced by serum / growth factor deprivation, and increased the S phase by FACS analysis with enhanced BrdU / Ki-67 labeling index. Transwell assay showed the migration of NSCs toward SDF-1 (500 ng/ml) gradient by 30% increase when compared to the control. Pre-incubation of neutralizing anti-CXCR4 antibody blocked the effects of SDF-1 on human NSCs. In this study, we confirmed the expression of CXCR4 in human NSCs, which mediate the migration of NSCs according to the SDF-1 gradient. Strategies to modulate the SDF-1/CXCR4 signaling may improve homing and engraftment of NSCs to brain.