Exosomes in disease and regeneration: biological functions, diagnostics, and beneficial effects

Abstract

Exosomes are a subtype of extracellular vesicles. They range from 30 to 150 nm in diameter and originate from intraluminal vesicles. Exosomes were first identified as the mechanism for releasing unnecessary molecules from reticulocytes as they matured to red blood cells. Since then, exosomes have been shown to be secreted by a broad spectrum of cells and play an important role in the cardiovascular system. Different stimuli are associated with increased exosome release and result in different exosome content. The release of harmful DNA and other molecules via exosomes has been proposed as a mechanism to maintain cellular homeostasis. Because exosomes contain parent cell-specific proteins on the membrane and in the cargo that is delivered to recipient cells, exosomes are potential diagnostic biomarkers of various types of diseases, including cardiovascular disease. As exosomes are readily taken up by other cells, stem cell-derived exosomes have been recognized as a potential cell-free regenerative therapy to repair not only the injured heart but other tissues as well. The objective of this review is to provide an overview of the biological functions of exosomes in heart disease and tissue regeneration. Therefore, state-of-the-art methods for exosome isolation and characterization, as well as approaches to assess exosome functional properties, are reviewed. Investigation of exosomes provides a new approach to the study of disease and biological processes. Exosomes provide a potential "liquid biopsy," as they are present in most, if not all, biological fluids that are released by a wide range of cell types.

Keywords: exosomes; methods; stem cells therapeutics.

Fig. 1.

Exosome isolation using size exclusion chromatography (SEC). Endothelial cells were cultured in medium containing 5% exosome-depleted FBS. The supernatant was collected and ultrafiltered after 24 h and then processed in SEC with 10 mL of bed volume. Each 500 μL of fraction was collected after the sample was added on top of the column. A: protein concentration of each fraction was determined using Nanodrop. B: Western blot was performed using 2 separate gels to detect the distribution of vast number of proteins and exosomes in fraction 5–30. Ponceau red stain confirmed that the vast number of proteins were eluted in later fractions, whereas anti-CD63 detected exosomes in early fractions. C, parent cell lysates as positive control. C: nanoparticle tracking analysis confirmed the exosome sizes in F9 (left) and F10 (right).

Fig. 2.

Engineering of the exosomal cargo is feasible to study mesenchymal stem cell (MSC) exosomes’ regenerative properties and may enhance regenerative efficacy in myocardial injury. Figure shows some examples that modulating or overexpressing miRNAs or proteins in MSC exosomes can protect the heart from ischemia injury directly through reducing cardiomyocyte apoptosis (238) and promoting endothelial angiogenesis (121) or indirectly through immunomodulation, such as M₂ macrophage polarization (243) or regulatory T (Treg) cell activation (221).

Fig. 3.

Distribution of extracellular vesicle (EV) publications across stem cell classes. A and B: PubMed searches using key terms exosomes, microvesicles, extracellular vesicles, stem cells, MSCs, HPCs, NSCs, iPSCs, ESCs, CSCs, satellite cells, and intestinal stem cells were used to determine the fraction of EV publications associated with different types of stem cells. MSC, mesenchymal stem cell; HPC, hematopoietic progenitor cell; NSC, neural stem cell; iPSC, induced pluripotent stem cell; ESC, embryonic stem cell; CSC, cancer stem cell.