Study On The Magnetic Resonance Imaging Of Exosomes In Vivo

Exosomes are one of the extracellular vesicles with lipid bilayer secreted from most leukaryotic cells.Exosomes can be isolated from cell culture medium,blood,urine,breast milk and other body fluids.Exosomes contain specific biologically active substances from parental cells,such as nucleic acids,proteins and lipids,so exosomes derived from different cells have different physiological functions.Exosomes can interact with adjacent or distant target cells through transmission by paracrine activity or blood,which enable molecular signals of exosomes to transfer to cells and then mediate cell interaction and communication.Numerous reports indicate that exosomes are not only deeply involved in many important physiological and pathological processes,such as immune response,apoptosis,cell migration,angiogenesis,inflammatory response and so on,but also can be used in therapy,drug delivery,tumor biopsy and other clinical research.Hence,in order to be able to gain knowledge of exosomes’ mechanism of action,biodistribution,pharmacokinetics and uptake in vivo and answer other similar questions,it is vital to develop methods of imaging the exosomes in vivo.In vivo imaging of exosomes could serve as a powerful tool for research because it allows researchers to peer deeply within living subjects and produces tremendous opportunities to understand how diseases develop and how therapies work regarding with exosomes.The current available technologies for in vivo imaging of exosome include different methods and modalities.Magnetic resonance imaging(MRI)is regarded as an ideal technique that delivers no radiation burden and provides excellent soft tissue contrast and spatial resolution for deep tissues with multiple parameters.This technique also has a large arsenal of functional and anatomical contrast mechanisms.To date,various attempts to visualize exosomes in vivo by MRI have been reported.Due to the exosomes’ small size and their composition,which is similiar to that of body cells and therefore lack of contrast.Hence,to visualize exosomes in vivo by MRI,considerable efforts have been devoted to develop exosomes’ labeling strategies.The current labeling technologies are exogenous labeling pathways.Exogenous labeling is based on loading exosomes with external artificial MRI contrast agents.This type of labeling allows assess the fate of the administered exogenously labelled exosomes via in vivo imaging modalities such as MRI,while it hardly applies to parent cell derived exosomes in living organisms.An efficient endogenous label technology that can be used to explore exosomes biogenesis pathway and their role in cellular communication in living organisms with MRI is still an unmet need.The aim of this study was to originally develop a platform technology for produce endogenously labeled exosomes by genetic engineering of exosome producing cells with viral vectors expressing genes for MRI reporter protein.We speculated that labeling exosomes with the MRI reporter protein that enhance the contrast and could be detected by MRI without additional exogenously contrast agents.Therefore,we selected two proteins,namely,ferritin heavy chain(FTH1)and lactadherin(LA).FTH1 functions as an MRI reporter and LA is a membrane-associated protein located on the outer surface of exosomes.We designed a fusion protein of FTH1 and LA through transgene methods,endogenously labeled exosomes were visualized in vitro and in vivo by MRI.This innovative labeling approach achieve to visualize endogenously labeled exosomes with MRI.Furthermore,the present study innovatively proposed an exogenous labeling method based on covalent-bonding between exosomes and gadopentetate dimeglumine(Gd-DTPA)to avoid the potential side effects caused by current exogenous labeling pathways.In summary,we systematically developed endogenous and exogenous labeling pathways to visualize exosomes in vivo through MRI.The exogenous labeling strategy was widely cited by peers,which could serve as a powerful tool to peer deeply within living subjects and produces tremendous opportunities to understand the role of exosomes in various pathophysiological conditions.