Cardiac myocyte exosomes: stability, HSP60, and proteomics

Abstract

Exosomes, which are 50- to 100-nm-diameter lipid vesicles, have been implicated in intercellular communication, including transmitting malignancy, and as a way for viral particles to evade detection while spreading to new cells. Previously, we demonstrated that adult cardiac myocytes release heat shock protein (HSP)60 in exosomes. Extracellular HSP60, when not in exosomes, causes cardiac myocyte apoptosis via the activation of Toll-like receptor 4. Thus, release of HSP60 from exosomes would be damaging to the surrounding cardiac myocytes. We hypothesized that 1) pathological changes in the environment, such as fever, change in pH, or ethanol consumption, would increase exosome permeability; 2) different exosome inducers would result in different exosomal protein content; 3) ethanol at "physiological" concentrations would cause exosome release; and 4) ROS production is an underlying mechanism of increased exosome production. We found the following: first, exosomes retained their protein cargo under different physiological/pathological conditions, based on Western blot analyses. Second, mass spectrometry demonstrated that the protein content of cardiac exosomes differed significantly from other types of exosomes in the literature and contained cytosolic, sarcomeric, and mitochondrial proteins. Third, ethanol did not affect exosome stability but greatly increased the production of exosomes by cardiac myocytes. Fourth, ethanol- and hypoxia/reoxygenation-derived exosomes had different protein content. Finally, ROS inhibition reduced exosome production but did not completely inhibit it. In conclusion, exosomal protein content is influenced by the cell source and stimulus for exosome formation. ROS stimulate exosome production. The functions of exosomes remain to be fully elucidated.

Exosomes and Cardiac Repair After Myocardial Infarction

“…A recent work from the same group demonstrated that pathological changes in the environment, including fever, changes in pH, hypoxia, and ethanol treatment, alter the rate of exosomes secretion and the protein content of exosomes from adult cardiomyocytes. 54 Furthermore, the authors have shown using the mass spectrometry analysis of adult primary cardiomyocyte-derived exosomes that the protein content of cardiac exosomes differ significantly from other types of exosomes described in literature and contain cytosolic, sarcomeric, and mitochondrial proteins. Similar observations were made by 2 independent reports demonstrating the release of TNF-α 82 and HSP20 83 via exosomes from cultured cardiomyocytes.…”

“…Interestingly, cardiomyocytes, which were initially considered as not-so-secretory cell type, have now been suggested to secrete exosomes. 49,53,54 In this context, the investigation of the role of exosomes in myocardial remodeling and repair is potentially important. Exosomes may provide the underlying mechanisms by which the damaged heart communicates with other tissues and organs to initiate the repair process, and how stem/progenitor cells repair and regenerate the myocardium.…”

Erratum: Inflammatory processes in cardiovascular disease: a route to targeted therapies

“…They have been shown to be important in cell-to-cell signalling, including in the context of inflammation. Extracellular vesicles carry a variety of cell-derived molecules including proteins 82 , mRNA, and microRNA 83 , and include exosomes (30-100 nm), multivesicular bodies (also called ectosomes or microparticles: 100-1,000 nm) 84 and apoptotic bodies (1-5 μm) 85,86 . Extracellular vesicles are continually produced by all cell types and, in the setting of AMI, those from endothelial cells and platelets have been shown to have roles in homeostasis of the cardiovascular system including coagulation 87 and tissue repair 88 .…”

Exosomes: scytales in the damaged heart

“…For this reason, in vitro studies have been very helpful not only providing evidence of exosome secretion but also in identifying the exosomal content and function from specific cell types. Early reports using primary cardiomyocytes and relevant cell lines have provided evidence of exosome secretion and detected nucleic acid-containing microvesicles/exosomes in the cell media, which could reprogram fibroblast gene expression (9,10). These investigations introduced a new concept in cardiac cell-cell communication, proposing that exosomes generated by cardiomyocytes are able to transfer protein or genetic information to neighboring cells of the heart.…”