Effect Of Stromal Cell-Derived Factor-1 On The Migration Of RMSCs Transplanted After Cerebral Ischemia

Objective To observe the therapeutic benefit of intravenous administration of rat mesenchymal stem cells(rMSCs)after cerebral ischemia in adult rats, which include the improvement of neurological function, the migration of rMSCs to infarct focus, and the differentiation of rMSCs, the effect of Stromal cell-derived factor-1 (SDF-1) on the migration of Mesenchymal Stem Cells(MSCs), and to explore the possible mechanism of this effect under the condition of brain ischemic injury.Methods Adult male SD rats were subjected to transient (2 h) middle cerebral artery occlusion (MCAO). rMSCs or PBS were infused into tail vein at 24 h after MCAO respectively. Functional outcome measurements using the modified Neurological Severity Scores (mNSS) were performed at 24 h post-MCAO, 1 week and 2 weeks post-transplantation respectively. Immunohistochemical staining and immunocyto- chemistry were used synchronously to identify rMSCs and their differentiation markers in the brain sections and the cultured rMSCs in vitro. Effects of SDF-1 on the migration of cultural rat MSCs (rMSCs) and N9 microglial cells were observed by counting migrated cells and by calculating the migration indexes to show the difference of rMSCs migration under the conditions with or without the existence of SDF-1. CTO-labeled rMSCs were injected into the tail vein of rat with middle cerebral artery occlusion (MCAO). The migration and congregation of labeled cells in the injured region of brain sections were observed under fluorescence microscope. Anti- CXC chemokine receptor 4 (Anti-CXCR4) antibodies were used for blocking studies, and the expressions of CXC chemokine receptor 4(CXCR4)in rMSCs were observed with RT-PCR and flow cytometry respectively.Results There was significant neurological function improvement in rats treated with rMSCs compared with that of control group, as evidenced by mNSS scores (p<0.001). After transplantation, rMSCs were survived and localized around the ischemic core and its boundary zone, and a few rMSCs expressed nestin, NF-200 and GFAP, but there were no such expression in rMSCs cultured in vitro. In vitro, the migration indexes of rMSCs and N9 microglial cells in the SDF-1 groups were significantly higher as compared with the medium controls(P<0.01). The CXCR4 antibody blocking significantly impaired the SDF-1 chemotaxis. In vivo, labeled rMSCs mainly migrated and congregated around the injured region in the rMSCs transplantation groups. The CXCR4 antibody also significantly impaired both the migration and congregation of rMSCs.Conclusions Intravenous administration of rMSCs can promote the neurological functional improvement in rat stroke model. rMSCs can survive and localize to the ischemic area of the brain, and a few cells express the phenotypic protein marker of neural cells. The benefit of intravenous administration of rMSCs are no brain injury and better distribution of grafted cells.The results demonstrate that the chemotactic effect of SDF-1 on the MSCs is introduced by CXCR4. Although only small proportion of rMSCs expresses active extracellular CXCR4 receptor,there are higher level intracellular expression of CXCR4. SDF-1 secreted from injured brain tissue may be responsible for the chemotaxis and congregation of MSCs . This phenomenon will be significant in the therapeutical research of acute injury .