Expression of SDF-1-CXCR4 axis and an anti-remodelling effectiveness of foetal-liver stem cell transplantation in the infarcted rat heart.

SDF-1, a chemokine secreted by injured tissues, may be instrumental in chemoattracting CXCR4(+) stem cells (SCs) for repair of infarcted myocardium. We hypothesize that the myocardial SDF-1 expression determines also the engraftment and beneficial effects of SCs transplanted into the infarcted heart. Myocardial infarction (MI) was induced in rats by coronary artery ligation. The animals were either sacrificed at 2, 7, 16, 21 or 28 days after MI or were re-operated at 2, 7 or 14 days after MI to receive SCs transplantation, and were sacrificed 14 days later. SCs transplantation consisted of 3 x 15 microl injections of SCs isolated from foetal rat liver (FLSCs) into the myocardium bordering the infarction zone (5 x 10(6) cells/heart, labelled with PKH2 Green Fluorescent Cell Linker, approximately 20% CXCR4(+)). In the MI border zone, SDF-1 and CXCR4 immunostaining was transiently increased after MI, picking at 2 days and down regulating to the sham level by 21 days after MI. Simultaneously, an increased incorporation of CXCR4(+) and CD133(+) cells into capillaries was evident. AMD1300, a blocker of CXCR4, prevented the post-MI expression of CXCR4. In the MI border zone, the cardiomyocyte cross-sectional diameter increased and capillary/cardiomyocyte ratio decreased systematically during the 28 post-MI days, while an interstitial collagen accumulation demonstrated transient increase. FLSCs did not survive in the non-infarcted hearts. In infarcted hearts, FLSCs survived best when they were injected at 2 days after MI. The survival was negligible again when the injection was performed at 14 days after MI. FLSCs transplanted at 2 days after MI caused a further rise in SDF-1, CXCR4, and CD133 expression, compared with the untreated infarcted hearts. Only FLSCs transplanted at 2 days, but not later, attenuated cardiomyocyte hypertrophy and increased capillary/cardiomyocyte ratio in the MI border zone. These results suggest that myocardial signalling for homing of the endogenous and the exogenous SCs is transiently activated early after MI, that SDF-1 is instrumental in this process, and that there is only a narrow time-window after MI when SCs transplantation results in their efficient myocardial engraftment and beneficial anti-remodelling effect.