Published at Rejuvenation Science News (RSN)
Highly Purified Human Extracellular Vesicles Produced by Stem Cells Alleviate Aging Cellular Phenotypes of Senescent Human Cells
Abstract
Extracellular vesicles (EVs), including exosomes and microvesicles, mediate intercellular communications and exert various biological activities via delivering unique cargos of functional molecules such as RNAs and proteins to recipient cells. Previous studies showed that EVs produced and secreted by human mesenchymal stem cells (MSCs) can substitute intact MSCs for tissue repair and regeneration. In this study, we examined properties and functions of EVs from human induced pluripotent stem cells (iPSCs) that can be cultured infinitely under a chemically defined medium free of any exogenous EVs. We collected and purified EVs secreted by human iPSCs and MSCs. Purified EVs produced by both stem cell types have similar sizes (∼150 nm in diameter), but human iPSCs produced 16‐fold more EVs than MSCs. When highly purified iPSC‐EVs were applied in culture to senescent MSCs that have elevated reactive oxygen species (ROS), human iPSC‐EVs reduced cellular ROS levels and alleviated aging phenotypes of senescent MSCs. Our discovery reveals that EVs from human stem cells can alleviate cellular aging in culture, at least in part by delivering intracellular peroxiredoxin antioxidant enzymes. Stem Cells2019;37:779–790
Significance Statement
Recently, increasing evidence has supported the idea that mesenchymal stem cell (MSC)‐derived extracellular vesicles (EVs) opened a new avenue for treating tissue injury. However, a major bottleneck in using MSC‐derived EV‐based applications in clinics is the inefficient production and purification of clinical‐grade EVs. Surprisingly, recent results demonstrate that human induced pluripotent stem cells (iPSCs) produce great numbers of EVs under a defined culture condition, and the concentration is much higher than by MSCs. Furthermore, this study investigated the activities of iPSC‐EVs and found that purified EVs from both stem cell types alleviate aging phenotypes of senescent MSCs. These EVs also alleviate progerin‐induced senescence in premature aging cell model. Overall, the delivery of human iPSC‐EVs attenuated cell aging and promoted cell proliferation, suggesting that highly purified EVs from human iPSCs may represent a cell‐free approach for treating aging and degenerative diseases.
Introduction
Extracellular vesicles (EVs), including exosomes and microvesicles, are heterogeneous populations of naturally occurring nanosized vesicles released by almost all cell types 1. They are enclosed by a lipid bilayer and range in size from a diameter from roughly 30 to 150 nm for endosomal system‐derived exosomes and ∼100–1,000 nm for cell surface‐shed microvesicles 2. EVs have emerged as novel and important players in intercellular communication, mainly through their ability to transfer biological content, consisting of proteins, lipids, and nucleic acids, to recipient cells 3, 4. Recent research efforts have focused on leveraging EVs as a powerful therapeutic tool in tissue repair and regeneration 5-7. Mesenchymal stem/stromal cells (MSCs) are one of the most commonly used cell types for classic cell therapy, as well as for potential EV‐mediated therapies without using intact donor cells 8. MSC‐derived EVs have opened a new avenue for treating tissue injury in cardiovascular diseases 9, radiation damage to bone marrow hematopoietic cells 10, fracture healing 11, and neurodegeneration 12. Despite these advances, a major bottleneck of MSC‐derived EV (MSC‐EV)‐based applications in clinics is the inefficient production and purification of clinical‐grade EVs. Cultured MSCs, especially those derived from adult tissues, have a limited cell proliferation capacity even under rich culture conditions, that is, supplemented by fetal bovine serum (FBS) or human platelet lysates. However, FBS and platelet lysates also contain abundant EVs. Ongoing studies are evaluating the yields, functions, and EV production capacity of MSCs that are expanded with various defined media and other culture conditions 13, 14.
Unlike postnatal somatic cells, including MSCs, human induced pluripotent stem cells (iPSCs) can be expanded in culture indefinitely while maintaining full developmental potential. In the past several years, completely defined culture medium was developed to expand human iPSCs on standard cell culture vessels coated with recombinant human vitronectin proteins 15. We and others have shown evidence that the Essential 8 (E8) media system maintains the pluripotency and genomic stability of human iPSCs after extensive culture 15, 16. With this recent breakthrough, it is no longer a major hurdle to expand human iPSCs efficiently under clinically compliant culture conditions. This highly defined and efficient iPSC culture system also makes it much easier to analyze numbers and functions of EVs made by human iPSCs 17. However, very few studies describe the properties and functions of human iPSC‐derived EVs 13, 18, 19, as compared with dozens of papers on MSC‐EVs 8. Additionally, most published applications of EVs used EVs from iPSC‐derived committed cell types such as MSCs and cardiomyocytes instead of EVs from iPSCs 20-23. However, the EV preparations (mainly by concentration using ultracentrifugation and polymer‐mediated precipitation) in these previous studies were relatively impure, containing undefined soluble and aggregated proteins 24, 25.
In this study, we examined physical properties and biological functions of iPSC‐EVs in comparison with MSC‐EVs. Following international standards for EV characterization and purification 24, 25, we obtained highly purified EVs from both cell types, although many more were produced by human iPSCs. Using two different cellular senescence models, we observed that highly purified iPSC‐EVs and MSC‐EVs alleviated cellular senescence and promoted cell growth. Our results suggest that purified EVs from human stem cells may represent a cell‐free approach for attenuating aging and treating degenerative diseases.
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F U L L T E X T : Stem Cells Journal
Edited by Engadin, 10 June 2019 - 08:33 PM.
