Improved Myocardial Metabolism And Function After Induced Pluripotent Stem Cells Transplantation

Myocardial infarction (MI) is a major cause of morbidity and mortality worldwide. Although conventional therapeutic approaches such as interventional treatments, pharmacotherapy, and surgery can improve cardiovascular function to a certain degree, their therapeutic outcomes are still limited due to the inability to save damaged or dead myocardial cells. Recently, the rapid progress of stem cell technologies has triggered an increasing interest in the use of pluripotent stem cells in cardiovascular repair. Embryonic stem cells (ESCs) can differentiate into multiple functional cardiac thical controversy. However, its clinical application has been greatly limited because of the risk of immune rejection and ethical controversy. Hence, it is necessary to find an alternative source of pluripotent cells to replace ESCs.The discovery of pluripotent stem cells (iPSCs) is the revolutionary breakthrough. In 2006, iPSCs can be generated by transduction of defined transcription factors (Oct3/4、Sox2、Klf4、c-Myc 4) from adult somatic stem cells through reprogramming and have been differentiated into the cardiac lineage, including myocardium and endothelial cells. This new cell type owns many similar features of ESCs, and can detour the risk of immune rejection and ethical issues. Although some studies have suggested that iPSCs might be an exciting cell source for renewing myocardium in vitro and improving cardiac function, to better understand the in vivo behavior and efficacy of iPSCs transplantation, a noninvasive, sensitive, repeatable and quantitative imaging modality is imperative. Positron emission tomography (PET) offers quantitative information and can be used to assess several variables (e.g., metabolism, perfusion). Since PET can be used for both cell trafficking and therapeutic response monitoring in clinical patients, it has been referred as one of the best-suited modalities to evaluate the therapeutic effect of stem cells. Particularly,18F fluorodeoxyglucose (18F-FDG) PET is a powerful tool to detect subtle changes of glucose metabolism in patients with cardiac disease.Although some initial studies examined cardiac functional improvement after ESCs or iPSCs transplantation, so far, no direct in vivo comparison has been made between these two cell types in the same MI model, and no side-by-side comparison has been done between serial PET imaging and serial immunofluorescence studies. Thus, in this study, we performed iPSCs and ESCs transplantation in a rat model of MI, evaluated the metabolic and functional recovery by using serial 18F-FDG micro-PET combined with micro-echocardiography, and confirmed by autoradiography, immunohistochemical and immunofluorescent analysis.Part 1:PET Molecular Imaging Demonstrates Dynamic Metabolic Changes after Stem Cells Transplantation in a Rat Model of Myocardial InfarctionWe evaluated the metabolic and functional recovery by using serial I8F-FDG micro-PET combined with micro-echocardiography, and confirmed by autoradiography, immunohistochemical and immunofluorescent analysis after iPSCs and ESCs transplantation in a rat model of MI. Animal model of MI was established by permanent coronary artery ligation. All animals were randomly assigned to one of the following three groups:phosphate-buffered saline (PBS) control, ESCs or iPSCs transplantation group. At Day 3 and Week 1,2,3, and 4 after cells delivery, all rats were accepted by 18F-FDG micro-PET, micro-echocardiograph scans and immunofiuorescence staining analysis. Post-mortem immunohistochemical staining and autoradiograpnic detection were performed after the last PET scan. From Week 1 to 4, changes of L/N ratio in the iPSCs and ESCs groups were significantly higher than that of PBS group (P< 0.001 and P< 0.001, respectively). It is noted that, compared to the ESCs, iPSCs group had lower 18F-FDG accumulation at Week 1 (P< 0.05) but increased significantly from Week 3 to 4 (P< 0.001). Compared to the PBS group, changes of LVEF increased significantly in both iPSCs and ESCs groups (P< 0.001 and P< 0.001, respectively) from Week 1 to 4. Interestingly, the change of LVEF in iPSCs group was significantly lower than that of ESCs group in the beginning (at Week 1, P< 0.001), but increased gradually and became significantly higher from Week 2 to 4 (P< 0.001). Serial immunofluorescence and immunohistochemical results exhibited survival and migration of iPSCs and ESCs during the 4-week experimental period. PET imaging findings were consistent to the echocardiographic, immunofluorescent results, which demonstrated significant metabolic and functional recovery after iPSCs and ESCs transplantation.Part 2:In vivo Dynamic Metabolic Changes after Stem Cells-derived Cardiomyocytes for Ischemia InjuryBased on the preliminary, we differentiated human ESCs and iPSCs into cardiomyocytes in vitro and to monitor and compare therapeutic effect these two kinds of cardiomyocytes using micro-PET and micro-echocardiography. MI was established by left lateral thoracotomy approach. Micro-PET and micro-echocardiography were performed on the third day and 1,2,3,4 weeks after stem cell-derived cardiomyocytes transplantation. Immunohistochemistry detection was done at the end of the last PET scan. Compared with PBS control group, significantly higher 18F-FDG accumulation and LVEF value were observed in two treatment groups from Week 1 to Week 4. However, considering the results of micro-PET and micro-echocardiography study, there was no statistically difference between hESC-CM and hiPSC-CM groups. Immunohistochemical finding demonstrated that transplanted hESC-CM and hiPSC-CM survived and improved myocardial metabolism and function.