Exosome in Cardiovascular Diseases: A Complex World Full of Hope

Abstract

Exosomes are a subgroup of extracellular vesicles containing a huge number of bioactive molecules. They represent an important means of cell communication, mostly between different cell populations, with the purpose of maintaining tissue homeostasis and coordinating the adaptive response to stress. This type of intercellular communication is important in the cardiovascular field, mainly due to the fact that the heart is a complex multicellular system. Given the growing interest in the role of exosomes in cardiovascular diseases and the numerous studies published in the last few decades, we focused on the most relevant results about exosomes in the cardiovascular filed starting from their characterization, passing through the study of their function, and ending with perspectives for their use in cardiovascular therapies.

Keywords: cardiovascular disease; exosomes; extracellular vesicle.

Figure 1

Release of exosomes (EXOs) and a sorting model. (A,B) Release of EXOs upon exocytic fusion of multivesicular bodies (MVBs) with the plasma membrane; arrows indicate the fusion profile. PM: plasma membrane; MVB: multivesicular body. Scale bars: 200 nm. (C) A proposed model for sorting of cargo into different MVB subpopulations. Different hypothetical MVB subclasses with distinct populations of intraluminal vesicles (red, green, and blue) are shown. Whether the MVBs contain a mixture of different intraluminal vesicles as depicted in the figure is not known. Sorting of cargo may already start within the biosynthetic pathway, at the plasma membrane, or within an endosomal compartment. Modified from Reference [1].

Figure 2

Electron microscopy of heart tissue. (A,B) Budding of the vessel wall to release the exosomes into the lumen (black arrows); (C) exosomes in the extracellular space; (D) exosomes released by myocyte fiber. Modified from Reference [16]. (E) Detection of proteins on cardiomyocyte (CM) EXO surface with flow cytometry. Mouse anti-caveolin-3 was detected on approximately 30% of EXOs (left), while mouse anti-flotillin-1 was detected on approximately 80% of EXOs. The distribution of EXOs presenting caveolin-3 and flotillin-1 indicates that the sample contains more than one population of EXOs. (F) Transmission electron microscopy of purified CM microvesicles (MVs)/EXOs. On the left, MVs/EXOs that display an electron-dense appearance are shown; on the right, MVs/EXOs that display an electron-lucent appearance are shown. Scale bar: 100 nm. Modified from Reference [15].

Figure 3

Schematic representation of protein content in EXOs from starved (+St), i.e., glucose-deprived, and non-starved (−St) CMs. CMs deprived of glucose change the protein pool contained in their EXOs, promoting their loading with proteins related to metabolic and catabolic processes, as well as blood vessel and cardiovascular development [24].

Figure 4

Summary of proteomics data acquired using a multidimensional protein identification technology approach. Venn diagrams representing the overlap of protein identifications between cardiac fibroblast (CF) whole-cell lysate, exosome, and secretome collected in (A) normoxic conditions and (B) hypoxic conditions. The number of proteins contained in the three fractions changed depending on the culture conditions. Modified from Reference [25].

Figure 5

Involvement of microRNA (miR)-146a in the impairment of heart function after myocardial infarction (MI). (A) Measurement of left-ventricular ejection fraction indicates that 146a knockout (KO) animals have severely impaired cardiac function and structure following acute MI compared to wild-type (WT) or 146a KO-R mice. (B) Representative Masson’s trichrome-stained sections of hearts from three groups show the different tissue regeneration after MI. (C–E) Morphometric analysis reveals impairment of cardiosphere (CDC)-mediated benefits as evident in pooled data for scar mass, viable mass, and infarct wall thickness (IWT) in hearts of 146a KO mice. * p < 0.05, ¶ p < 0.05; ** p < 0.01, and ¶¶ p < 0.01, *** p < 0.001, and ¶¶¶ p < 0.001 using Student’s t-test (* KO versus WT; ¶ KO versus KO-R). Data are represented as means and standard errors of the mean (SEM). Modified from Reference [39].

Figure 6

Engineering of extracellular vesicles (EVs). EVs can be engineered to load desired items, which can be carried out either endogenously or exogenously. Endogenous loading is achieved via transfecting parent cells strongly overexpressing miRNA or mRNA; this results in the production of EXOs that are already loaded with the elements of interest upon their collection. Exogenous loading allows the collection of drug-free EXOs which are then loaded with desired cargo molecules either via simple co-incubation with suitable cargo molecules or via active encapsulation with the help of certain procedures, such as electroporation. Modified from Reference [62].