Fundamental Role of Molecular Biology Techniques in Supporting Exosome Research and Applications

Here you will learn about how molecular biology techniques are fundamental in supporting the rising interest in exosomes and their varied applications.

Exosomes have recently gained increasing recognition for their vital roles in human health and disease. All cells make these extracellular vesicles that participate in intercellular communication by carrying diverse cargo, including nucleic acids, proteins, and lipids. And in delivering these payloads, they exert various effects, from impacting pregnancy to altering responses to cancer chemotherapy.

Exosome research is also moving more towards diagnostic and therapeutic applications that depend on molecular biology techniques for exosome characterization.
 

Exosomes are a type of extracellular vesicle. Their sizes range from ~40 to 160 nm, with an average diameter of ~100 nm. Among the most important characteristics of exosomes is that they carry an array of functional cargo—nucleic acids (DNA, RNA), proteins, amino acids, lipids, and metabolites—derived from their cell of origin. The beginning stages of exosome biogenesis occur in endosomes. They interact with intracellular vesicles and organelles to collect their various cargo and are then secreted by cells.

Figure 1. Basic information about exosomes, including their size and composition.

It remains a mystery why cells produce exosomes, but progress in this area of research has provided insight into some possible functions. One is to remove unnecessary cellular components to “clean up” cells. Another is to participate in intercellular communication by carrying contents that may affect other cells in health or disease.

Exosome-mediated, cell-to-cell communication spans a variety of biological roles, impacting pregnancy, immune responses, infections, metabolic and cardiovascular diseases, neurological disorders and diseases, and cancer.

Despite their significant contributions to health and disease, exosome research is still a relatively new field. Exosomes were first discovered in 1983 when two papers on the topic were published around the same time.¹ However, the name “exosome” was coined a few years later by Rose Johnstone.

The number of exosome-related publications has grown exponentially since 2010. Over the past 11 years, the number of exosome-related publications on PubMed rose from 282 to 5,073, representing a 30% compound annual growth rate (CAGR).

Since exosomes deliver contents that influence health and disease in positive and negative ways, they have become an area of interest for various applications. Naturally occurring exosomes provide a glimpse into the cellular mechanisms of diseases. 
 

In recent years, research has made it clear that exosomes are involved in regulating complex intracellular pathways. Therefore, significant focus has been placed on better understanding their roles and how we can harness their influence on these pathways for numerous applications.² Identifying novel mechanisms that regulate different phases of health and disease will propel corresponding applications for monitoring, diagnosing, and treating patients.
 

Exosomes affect reproduction and development. During pregnancy, cells communicate at various phases. The miRNAs in exosomes from semen, the placenta, blood plasma, and breast milk help maintain healthy conception and both fetal and postnatal development.

Exosomes can positively and negatively alter infection progression and the immune response. They present antigens and deliver nucleic acids, such as bacterial DNA, to trigger the innate immune response. Alternatively, when pathogens or their associated biomolecules enter exosomes, it can help them survive or thrive. For instance, some viruses may use exosomes to enter host cells. Another example is how DNA and small RNAs from the malaria pathogen Plasmodium falciparum found in exosomes may provide an advantage to the parasite.

Metabolic and cardiovascular diseases are also impacted by exosomes. Exosomes can carry metabolites like the peptide hormone adrenomedullin, inducing lipolysis and inhibiting insulin secretion. Additionally, certain exosomal miRNAs promote insulin resistance, while others can support cardiovascular health.

Exosomes can help or hinder the progression of neurological disorders. A key feature of exosomes relative to brain-related processes is their ability to pass through the blood-brain barrier, allowing them to enter a difficult-to-access but very important area of the body. In the brain, exosomes may alter the aggregation of abnormal proteins and help in clearing them (i.e., removing waste), however they are also known to carry tau and Aβ proteins, which are associated with Alzheimer's disease. At this time, their overall influence on neurological disease is still unclear.

An area of great interest for exosomes is their relationship with cancer tumor growth, metastasis, and resistance to therapy. Exosomal cargo has been implicated in neoplasia, including miRNAs in prostate and breast cancer, and mRNAs in prostate cancer. Diverse exosomal payloads, including nucleic acids, proteins, and metabolites, can enhance tumor growth. Surface proteins on exosomes can enhance or suppress metastasis, and exosomal miRNAs in breast cancer can promote metastasis. Additionally, metabolites in exosomes can fuel tumor growth due to their effect on the TCA cycle. Exosomes also carry nucleic acids, such as miRNAs in breast cancer and a long noncoding RNA (lncRNA) in renal cell carcinoma, that can increase cancer resistance to chemotherapy and antibodies.
 

Taking all these functions into account, it’s clear that exosomes have significant potential for numerous applications, including investigating healthy and diseased states.

When it comes to simply understanding healthy versus diseased states, it’s clear that exosomes carry information to provide new insight, as detailed above. Further research into the foundational impact they have in these areas is necessary.

All the applications discussed above require the isolation and characterization of exosomes.³Diverse techniques can be used for exosome isolation, including differential centrifugation, density-gradient ultracentrifugation, size exclusion, immunological methods, and microfluidics.

To understand exosomes in health and disease, they must be well-characterized. Much focus has been on physical characterization, including size and shape, but most applications depend heavily on knowing the payload and where and if it was delivered.

Exosomes commonly carry nucleic acids, proteins, amino acids, lipids, and metabolites. Nucleic acids seem to play a key role, therefore characterizing nucleic acid content is critical. Commonly used methods are PCR, RT-PCR, or sequencing. PCR and RT-PCR are relatively accessible, affordable, and easier to do than alternatives.

In addition to knowing what exosomes carry, the effects of exosome cargo must also be considered, so the methods to monitor and characterize the cellular and tissue response are also crucial. For example, gene expression analysis can reveal the differential expression of genes in cells with and without exosome content and/or delivery. PCR and RT-PCR are common and efficient tools for this purpose as well.
 

The vast importance of exosomes in the human body has recently come to light due to their wide-ranging impact on health and disease. Recent interest in exosomes has centered on their application to understanding health and disease states. These applications require basic molecular biology methods and skills to characterize exosomes. It is critical to use reliable, high-quality reagents in your experiments for this and any molecular biology-dependent application.

1. Harding CV, Heuser JE, Stahl PD. Exosomes: looking back three decades and into the future [published correction appears in J Cell Biol. 2013 Apr 29;201(3):485]. J Cell Biol. 2013;200(4):367-371. doi:10.1083/jcb.201212113
2. Kalluri R, LeBleu VS. The biology, function, and biomedical applications of exosomes. Science. 2020;367(6478):eaau6977. doi:10.1126/science.aau6977
3. Gurunathan S, Kang MH, Jeyaraj M, Qasim M, Kim JH. Review of the Isolation, Characterization, Biological Function, and Multifarious Therapeutic Approaches of Exosomes [published correction appears in Cells. 2021 Feb 22;10(2):]. Cells. 2019;8(4):307. Published 2019 Apr 3. doi:10.3390/cells8040307