Dynamic Changes Of Stromal Cell Derived Factor-1 In Ventricular Tissue After Myocardial Infarction

Objectives:The use of stem cells and cytokines to repair injured tissues after myocardial infarction is intensively studied by cardiovascular researchers in recent years.To make this treatment effective,there must be plenty of stem cells homing into the infarct and peri-infarct region first,then staying for an enough long time.As the key factor for promoting mobilization and homing of stem cells,stromal cell derived factor-1(SDF-1)plays an important role in the repairing treatment after myocardial infarction through the interaction with its receptor CXCR4.However, there have been diverse viewpoints about how SDF-1 changes after myocardial infarction in different studies at present,and the mechanism underlying it is even more poorly understood.In this study,we are going to establish a rat model of myocardial infarction,and analyze how the SDF-1 mRNA and protein expression level would change at different time after myocardial infarction,then compare the results with the non-infarct control.So as to provide a reference for deeper understanding of the pathophysiological changes after myocardial infarction,and discuss our inference about the mechanism for this change.Methods:70 wistar rats were use in this study.Left anterior descending coronary artery was ligated to set up the rats' myocardial infarction model.Rats were sacrificed at 1h,2h,6h,12h,1d,3d,7d,14d,28d after ligation(no less than 4 rats in each time point),then infarcted tissues were taken for SDF-1's protein and mRNA expression level detection.Cardiac tissues from left ventricular free wall of healthy rats were taken as control.Total RNA of rats' ventricular tissues were extracted by TRIzol agent;the quality of total RNA were examined by agarose gel electrophoresis; ultraviolet light spectrophotometer were used to determine the OD values at 260nm, 280nm and 310nm of total RNA,the purity of total RNA samples were analyzed by OD260/OD280 ratios,the concentration of total RNA samples were evaluated by OD260 values,the first strand of cDNA samples were synthesized by RT-PCR reaction,ultraviolet light spectrophotometer were used again to determine the OD values at 260nm,280nm and 310nm of cDNA samples,the OD260/OD280 ratios were used to analyze the purity of cDNA samples,the concentration of cDNA samples were evaluated by OD260 values,products of ordinary PCR reaction were taken for agarose gel electrophoresis in order to assess the quality of PCR primers and cDNA samples,then the relative expression level of SDF-1 in rats' ventricular tissues were detected by real-time PCR analysis.The rest ventricular tissues were homogenated by protein lysate,the concentration of total protein were assayed by Bicinchoninic Acid disodium(BCA)analysis,SDF-1's protein level in rats' ventricular tissues were detected by western blot analysis.Results:Compared with the control group,the mRNA expression of SDF-1 was significantly down regulated at different time points after myocardial infarction, this trend was sustained from 1 hour to 28 days after myocardial infarction.There's no statistic difference among the SDF-1 mRNA expression level of different time points after myocardial infarction.The protein level of SDF-1 had no change from 1 hour to 3 days after myocardial infarction compared with the control group,while it started to rise 7 days after myocardial infarction,reached 2.32 times as high as the control group's level.A 3.19 folds increase of SDF-1 protein level in infracted region was observed at 14 days after myocardial infarction,till 28 days after myocardial infarction,the SDF-1 protein level in infracted region was still slightly higher than control.Conclusions:The mRNA expression of SDF-1 was significantly down regulated in rat's ventricular tissues after myocardial infarction compared with non-infarcted control;while the protein level of SDF-1 in infarcted tissues started to rise 7 days after myocardial infarction,and it was still slightly higher than control till 28 days after myocardial infarction.This result hints that ventricular tissues cannot provide enough endogenous SDF-1 to mobilize stem cells for self-repair after myocardial infarction,the up regulation of SDF-1 proteins in the infarct area 7 to 28 days after myocardial infarction might be caused by the releasing of platelets. Supplying sufficient quantum of SDF-1 and stem cells at a proper time may exert a satisfying promotion towards the repair of myocardial infarction.However,the clarification of the specific mechanism for the changes of SDF-1 after myocardial infarction still relies on further investigation.