| Cardiovascular disease is a serious disease that affects people's health,and brings heavy economic and mental burden to patients,families and society.There are 17 millions people died of cardiovascular disease in the world every year,more than half of them died from myocardial infarction.In the past 10 years,China's incidence of myocardial infarction increased significantly,has been close to the international average level.China set up a “myocardial infarction treatment day” and determine each year in November 20 th as “China's 1120 myocardial infarction treatment day" in 2014.Myocardial infarction is a kind of myocardial ischemic disease caused by coronary artery spasm,atherosclerotic plaque hemorrhage and/or rupture and thrombosis.Angiogenesis is an important factor affecting the prognosis of myocardial infarction.And how to improve the blood supply of infarcted myocardial tissue has become a research hotspot in the treatment of myocardial infarction.A large number of studies have shown that VEGF is the most famous and the most remarkable biological molecules to promote angiogenesis.VEGF promotes the proliferation of endothelial cells through the high affinity receptor(tyrosine kinase receptor Flk-1 and fms-like tyrosine kinase receptor Flt-1)of endothelial cells and induce angiogenesis.However,due to the short half-life of VEGF in the blood(about a few minutes),intravenous administration of VEGF did not improve the cardiac function and angiogenesis after myocardial infarction.When Increasing the dose of VEGF showed a slight improvement in cardiac function,but it also produced serious adverse reactions(cancer,diabetic retinopathy,rheumatoid arthritis and atherosclerosis)in animal experiments.How to deliver VEGF to myocardial infarction area has become the most important research direction.It is an important tool to study the delivery system of VEGF targeted myocardial tissue,it is also a difficult problem to solve the drug delivery system of coronary atherosclerotic heart disease.Drug delivery system development needs to meet the following conditions: 1.preferably biocompatibility and safety,2.Easy to use in clinical practice,3.Highly targeted deliver efficiency,4.Higher drug loading rate,5.Drug activity protection.Based on the physiological and pathological characteristics of myocardial infarction,we screened the structure of myocardial infarction in vivo.The most significant pathophysiological feature of myocardial infarction is ischemic aseptic inflammation.Inflammatory cells and stem cell homing and exudation is an obvious characteristic of myocardial infarction.SDF-1 / CXCR4 axis of mesenchymal stem cells play an important role in chemotaxis,homing and MSC transplantation of infarcted heart.SDF-1 is secreted by the cells in the ischemic myocardium and regulate the recruitment of MSC.MSC migrated to infarcted myocardium along the SDF-1 concentration gradient by binding SDF-1 to CXCR4 on the surface of MSC.Since MSC is derived from blood,they have good biocompatibility.Therefore,we propose a VEGF delivery system based on the homing characteristics of mesenchyma stem cells.Mesenchyma stem cell surface engineering is an engineering method of surface grafting based on the characteristics of mesenchyma stem cell membrane.The surface characteristics of mesenchymal stem cells as follows: 1.The negative charge on the su rface of cell membrane;2.Lipophilic properties of cell membrane phospholipids;3.The surface molecules on the cell membrane.According to the characteristics of the mesenchyma stem cells,the surface engineering of mesenchymal stem cells can be divided into the following parts: 1.Layer by layer self-assembly of positively charged polyelectrolyte;2.Self-assembly based on Hydrophilicity and hydrophobicity;3.Grafting method based on antigen antibody reaction;4.Coupling grafting method based on the ch aracteristics of surface;5.Grafting method using chemical crosslinking method.Because of the immunogenicity of the third and fourth method,and the biocompatibility of the fifth method,we abandoned them in the research and used the first two methods.In order to reduce the impact on stem cells and keep good biocompatibility,we used the hydrophobic and electrostatic interaction loading VEGF and construct a cell membrane engineered drug delivery system of myocardial infarction.In order to improve the long-term existence of surface engineered mesenchymal stem cells in the infarct area and achieve sustained VEGF release,it is necessary to improve the microenvironment of the myocardial infarction area and the survival of stem cells.The spleen is an important hematopoietic organ in the embryonic period.It is the largest immune organ and a living large number of stem cells.A large number of studies have shown that the extracellular matrix of spleen plays an important role in the regulation of immune function,such as stem cell survival,paracrine,differentiation and so on.So We supposed that the extracellular matrix of spleen can improve the survival of stem cells homing,and then improve the heart function.We prepared the temperature sensitive(liquid at room temperature,and self assembled into glue at 37°C)spleen extracellular matrix hydrogel,which can be used as a minimally invasive interventional therapy.Therefore,we study the surface engineering of mesenchymal stem cells in the treatment of VEGF targeted myocardial infarction from four aspects.1.A study on the treatment of myocardial infarction with self assembled VEGF of mesenchymal stem cells.We developed a VEGF delivery system for the infarct area,this method is based on the MSC cells keep the characteristic of homing after layer by layer self-assembly,which improves the angiogenesis and heart function in the infarct area.The results showed that the MSC cells coated with layer by layer self assembled VEGF could continuously release VEGF in vitro,and had SDF-1 chemotaxis;In vivo experiments showed that the VEGF coated MSC was able to return to the infarct area,enhance cardiac function,increase blood flow,and promote angiogenesis.These preclinical studies have revealed that the applic ation of VEGF to the surface of MCS cells by layer by layer self-assembly may be a promising tool for noninvasive treatment of myocardial infarction.In contrast to other drug delivery systems,the use of layers of self-assembled VEGF to MSC cell surface has the following advantages: 1.MSC is the body's innate cells,because of its cell biocompatibility,has been used for cell therapy and drug delivery;2.The drug is encapsulated on the surface of MSC cells by layer by layer self-assembly,and it is shown that the drug can be released continuously and has a good pharmacokinetic effect;3.By wrapping up other drugs onto the surface of MSC,it may be possible to treat other diseases.2.Targeted therapy of mesenchymal stem cells grafted with VEGF in patient s with myocardial infarctionThe self-assembly of VEGF loaded mesenchymal stem cells as the package effect of layered chemokines and mesenchymal stem cell surface receptors,thereby weakening the mesenchymal stem cell homing ability and drug delivery efficiency.The purpose of this study is to improve the MSC homing of layer by layer self-assembly VEGF,and to improve the biological activity of VEGF,the first time we have prepared DMPE-PEG-Heparin grafted MSC.The experimental results show that the amphiphilic DMPE-PEG-Heparin can be grafted onto the phospholipid bilayer of the mesenchymal stem cell membrane through its lipophilicity.The binding of chemokines and adhesion molecules to the surface recptors of mesenchymal stem cells is the basis for the directional homing of mesenchymal stem cells.The chain like grafting method,rather than the lamellar self assembled polyelectrolyte layer,is helpful to maintain the homing ability of mesenchymal stem cells.The lamellar self assembled polyelectrolyte layer may weaken the directional migration ability of layer by layer self-assembly MSC by affecting the binding of chemokines to the membrane receptor of mesenchymal stem cells.In vitro experiments showed that heparin /VEGF loaded with VEGF had sustained release ability,and increased the half-life of VEGF in the infarct area.It plays an important role in the repair of VEGF during myocardial infarction.3.Study on the mechanism of improving the immune microenvironment of myocardial infarction by extracellular matrix hydrogelIn the first two parts of the study,we successfully constructed a layer by layer self assembly of mesenchymal stem cells and DMPE-PEG-heparin grafted mesenchymal stem cells(MSCs)with myocardial infarction targeting function and VEGF lo ading.Surface engineered mesenchymal stem cells have the ability to deliver VEGF to infarcted myocardium and participate in the repair of infarcted myocardium,improve angiogenesis in infarcted myocardium and improve cardiac function.But when the surface engineered mesenchymal stem cells home to the infarct area,the poor micro environment of infarct area will lead to the mesenchymal stem cell death,cleared by the immune system,thus affecting the sustained release drug delivery system of drugs such as VEGF.How to improve the microenvironment of myocardial infarction so as to avoid the removal of mesenchymal stem cells from the surface of immune inflammatory system has become an important research direction.The immune system plays an important role in the recovery of myocardial infarction.However,the deterioration of the immune microenvironment in the infarct area has become a critical issue.The microenvironment of the infarct area is an important target of drug therapy for cardiac repair,which is mainly composed of lymphoid cells and immune cells.The spleen is the largest immune organ in the human body,and its extracellular matrix plays an important role in the process of immune cells,lymph nodes,immune balance and so on.Therefore,we propose a hypothesis that the preparation of the extracellular matrix by the spleen tissue after the removal of the cells may improve the cardiac function by optimizing the microenvironment of the infarct area.In this study,we developed a temperature sensitive hydrogel derived from the extracellular matrix of the spleen,which exhibits the characteristics of self-assembly when injected into the body.The results show that the spleen hydrogel contains a variety of complex,the complex domain of these complexes may affect the immune function.Spleen hydrogel can promote the development of monocytes and lymphangiogenesis,thereby enhancing the cardiac function after myocardial infarction In vivo.Our results suggest that the use of biomaterials to improve the immune microenvironment may be a new technique for minimally invasive treatment of myocardial infarction.4.Study on the therapeutic effect of spleen extracellular matrix hydrogel on improving cardiac function by stem cellsIn the first two parts of the study,we successfully constructed a layer by layer self assembly of mesenchymal stem cells and DMPE-PEG-heparin grafted mesenchymal stem cells with myocardial infarction targeting function and VEGF loading.In the third part,the extracellular matrix hydrogel was prepared successfully.The results showed that the extracellular matrix hydrogel of spleen had the function of regulating immune microenvironment.Furthermore,we studied whether spleen cell extracellular matrix hydrogel could improve stem cells in the survival of myocardial infarction area,will provide new strategies and tools for future cell surface engineered stem cells and cell therapy.The spleen is an important hematopoietic organ in the embryonic period,and is an important organ of adult stem cells after birth.Many studies have shown that the extracellular matrix plays an important role in the survival,paracrine and differentiation of stem cells.EPC is an important cell for stem cell therapy because of its easy to separate and promote angiogenesis,So we chose EPC as a model molecule to study the effect of spleen extracellular matrix hydrogel on stem cell survival.In this study,we injected Spleen extracellular matrix hydrogel which contained EPC into the rat model of myocardial infarction,and investigated the effects of EPC on the survival and cardiac function.The results showed that EPC had a lower apoptosis rate and a better survival rate in the spleen extracellular matrix hydrogel.The animal experiments showed that spleen specific ECM hydrogel can effectively improve the survival of EPC and enhance the cardiac function. |
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