Exosomes, which function as intercellular messengers and can alter the bioactivities of recipient cells, have become a focus of research in recent years due to their unique properties for both diagnosis and therapy. Most cells secrete exosome into the extracellular space after multivehicular bodies (MVBs) fuse with the cell membrane and become extracellular vesicles (EVs) with diameters of 30–140 nm. The physical properties of some of these EVs are similar to exosome, such as their size and density, which makes it challenging to isolate exosomes.
The lack of exclusive biomarkers, the inefficient methods for separating exosomes, and the lack of high-resolution visualization techniques have limited our understanding of exosomes, despite significant efforts.
Reviewing current knowledge on exosome biogenesis and functions, as well as existing therapeutic applications and emerging technology in exosome characterization and isolation, this article aims to present a summary of the current knowledge on exosome biogenesis and biochemical properties. We will also discover the limitations that prevent the successful isolation, purification, and characterization of exosomes. Finally, we will be able to propose future research topics.
The biogenesis of exosomes differs from those of other types of EVs. Exosomes, on the other hand, are formed during the process of endosomal maturation, when the plasma membrane of the endosomes invaginates.
Multivehicular bodies (MVBs), or late endosomes, contain a population of intraluminal vesicles (ILVs) which when released form exosomes. MVBs either travel to the cell membrane and fuse with it, releasing their contents into the extracellular environment, or travel to the lysosome and are digested. Stress triggers exosome formation by regulating p52, though it is unknown if this also increases ILV formation under hypertoxic or genotoxic conditions.
Components And Cargo Of Loading Mechanisms
As a biomarker and a delivery vehicle for drugs, exosomes remain of great interest. Knowing the contents of these files and how they load is important. Despite this, we still don’t fully understand how they work.
ALIX is renowned for binding to the ESCRT system and to Syndecan-1, which then binds to syndics via the PDZ domain.
Sequestering cargo is typically mediated by the association of cargoes with heparan sulfate proteoglycans of syndical following trimming by heparinize of the heparan sulfate.
In addition, exosomes have different protein and RNA compositions in cells. In spite of the fact that these two exosome populations appear to be separate, we do not know what the difference between them is or where their origins lie.
Biomarkers Of Exosomes
Exosomes are currently being studied for their potential to be used both as biomarkers and delivery systems for therapies. This is extremely important because the molecules can cross the blood brain barrier. Fluid biopsies, for example, are minimally invasive procedures that are required to analyze biomarkers in the blood or urine. MiRNA can also be used as a biomarker with these cargoes because they are well protected against degradation. Previously, miRNA could not be used with these cargoes as it was easily degraded.
The biology of exosomes has been studied extensively in cancer research. By using exosomes and the contents as well as surface proteins, it may be possible to detect cancer earlier, therefore increasing survival and prognosis.
A number of overexpressed proteins were detected in the exosomes from non-small cell lung cancer including epidermal growth factor receptors (EGFR), placental alkaline phosphatases (PLAPs), and leucine-rich alpha-2-glycoproteins (LRG1).
A Cancer’s Exosomes
Exosomes are normally released by cells in a normal manner, but cancer cells release exosomes at high levels, which serve as ideal fuel for cancer development. After they are released from the tumor cell, tumor exosomes circulate in the extracellular space until they reach their intended targets. Exosome cargo contents are protected from degradation by enzymes or other extracellular conditions during this process by membrane bilayers, which act as lipid bilayers.
As tumor exosomes are taken up by recipient cells, they modify the cell function and phenotype, impacting both nearby and distant non-tumor cells, so as to create a microenvironment that is conducive to cancer proliferation, dissemination, and metastasis. Cancer progression is complex, and exosomes play an important role at every step of the process. Several key aspects of how exosomes affect cancer development are discussed in sections III A–III C.
Tumor Growth And Microenvironment Altered By Exosomes
Exosomes generated by cancer cells have been found to stimulate tumor growth by directly activating the signaling pathways responsible for sustaining tumor proliferation, such as Pi3K/AKT (phosphorylated phosphatidylinositol 3-kinase/protein kinase B) and MAPK/ERK (mitogen-activated protein kinase/extracellular signal-regulated kinase).
We found that exosomes were capable of promoting cell proliferation by activating P13K/AKT and MAPK/ERK pathways in gastric cancer cells. CD97 is responsible for mediating proliferation in gastric cancers through the MAPK pathway, according to another study.
THE Opportunity For Exosome-Based Therapeutics
Exosomes have been extensively studied for their potential therapeutic role in disease propagation, cancer proliferation and metastasis. We can actually stop the progression and spread of diseases by targeting disease derived exosomes.
Exosomes also possess a great deal of potential as natural carriers for therapeutic molecules due to their native structure and unique cellular function. Using exosomes as therapeutic targets and natural delivery vehicles for drugs and genes is discussed in Sections IV A and IV B.
In conclusion, further advancement in this field will require the development of efficient and reliable isolation methods. It is vital that basic research and emerging technologies are integrated to maximize the potentials of these technologies, which lay the foundations for their therapeutic applications.