The Emerging Roles of Exosomes in Disease Modelling
A small advancement in cell biology is primed and ready to have a significant impact on how we reckon about and study diseases. Traditionally, the most common approaches for studying the progression of the disease have included establishing an animal model and examining tissue histology and biochemistry for changes in protein expression. Exosomes are membrane-bound, tiny vesicles (30–150 nm) that are discharged by cells into the fluid that exists among the cells. Exosomes are composed when endosomes are split off and merged with the plasma membrane; as a result, they include a selection of the DNAs, RNAs, and proteins contained in the cell that produced them, including cell surface indicators.
Exosomes can be isolated, usually from a liquid biopsy, and then their component macromolecules can be examined in order to make judgments about the condition of the cells, organs, or organisms from which they originated. This demonstrates that it is possible to cultivate disease-specific cell lines, isolate exosomes from a controlled cell culture medium, and profile the proteins, DNAs, and RNAs found therein instead of harvesting a mouse’s kidney, cutting serial sections, performing a Western blot, and staining with a phenotypic marker of disease. Exploring the realm of exosomes is recommended because of its reduced cost, higher throughput and human-relevant, disease-specific information.
Exosomes and Diseases
Exosomes are emitted by the majority, if not all, of healthy human cells as well as by sick, stressed-out, and diseased cells. Therefore, it stands to reason that the sick, stressful, or unhealthy condition will reflect in the exosomes that these cells release. Furthermore, circulating exosomes from individuals with specific disorders can contain abnormal proteins and disease-promoting nucleic acids, as shown by liquid biopsies. It has even been shown that these conditions can spread from one organism to another after an exosome transfusion.
The constituent of exosome macromolecules changes as an individual passes from being in good health to having a disease, reflecting the altered homeostasis brought on by the disease burden and more exosomes are released, a phenomenon brought on by an increase in intracellular sodium that may be an attempt to signal cellular distress to neighbouring cells. Therefore, collecting and characterising exosomes from cells or tissues of a known disorder can reveal not only the biological purpose of these cellular messengers but also the labels of potential therapeutic targets that were previously unknown.
In vitro Reiteration of Disease
Although some exosome disease research is done using fluid samples taken from patients (blood, saliva, urine, etc.), there is another way to examine the exosomal profile of different diseases. Exosomes from cell lines in culture have been shown to release into the culture media, and data suggest that patient-derived exosomes and exosomes from cell lines can be used to make similar diagnoses. Exosome profiles of cell lines isolated from patients with a particular condition appear to be stable throughout time, releasing exosomes with the same content on a regular basis. It is now possible to extrapolate from exosomes generated by cell lines to exosomes derived from liquid biopsies, and this has allowed for the use of non- or minimally invasive fluid samples as diagnostics for exosome biomarkers of several disorders.
Cell lines are produced using tissue samples, frequently following a surgical tissue biopsy or the removal of diseased tissue. Due to the natural immortalization shown by tumour cells, some disease-specific cell lines can survive in culture for long periods of time. However, cells can be made to become immortal in the lab by increasing the expression of an oncogene. In this manner, healthy and normal cell lines are produced. Primary cells, on the other hand, are not immortal and can only undergo a limited number of divisions before senescence or cell death. Due to the inability to regulate and repeat the preparation of primary cells, they are not the optimum reliable source of exosomes for investigation in cell culture.
Phenotypic Analysis of Exosomes
Exosome production and isolation is just the initial step in the in vitro disease characterization process. The next stage is profiling the isolated exosomes with a number of phenotypic markers in order to identify the cell from which they were extracted and to assess any changes between the profiles of the cell lines representing the diseased and healthy states. Antibodies that detect proteins in the lipid bilayer and vesicular compartment of exosomes are utilised as phenotypic markers to describe the profiles of these cellular components.
There are various markers that are used to identify exosomes, even if there is no agreement on a panel of markers that can confirm an exosome’s identity. Exosome markers include those like CD9, C81, and MHC Class 2, which are generally recognised. Exosomes can also be stained for cell line- or lineage-specific markers to pinpoint the exact cell type from which they were produced in order to obtain detailed information about the cell of origin.
Exosomes may be studied by immunofluorescence, electron microscopy, Western blotting, or ELISA. Imaging flow cytometry is a popular technique for the investigation of phenotypically characterized exosomes, which can validate the size and form of the exosome.
Exosomes produced from cell lines have various advantages over conventional disease-state analysis techniques, including higher throughput, reduced cost, and direct application to human disease.
