Over the past 30 years, extensive research has given science an in-depth look into how the cells in the body communicate with one another. The short answer is that all cells send out small nanoparticles — called exosomes — as messengers that circulate in the body’s fluids and are absorbed by target cells.
Different surface receptors tell the exosomes where to go and which cell will be destined to absorb them. The exosomes are 30-150 nm in size or about 1,000th the size of a regular cell.
What Makes Up Exosomes
The content in an exosome is derived from cell constituents of the parent cell and is essentially identical to that cell with growth factors, enzymes, receptors, transcription factors, matrix proteins, and intracellular signaling mediators as well as messenger RNA (mRNA, the blueprint for protein production) and microRNA (miRNA, an important intracellular signaling mediator).
Circulating proteins are degraded to amino acids by proteases, but all components in the exosomes are protected in the blood plasma from degradation by a double-layer lipo-protein cell wall — the same type of cell wall that surrounds regular cells.
One very important difference between exosomes and cells is that exosomes do not contain any DNA or human leukocyte antigen (HLA) class II antigens, and therefore, exosomes do not induce any immune response. In addition, exosomes do not induce any graft-versus-host immune response.
Exosomes and Stem Cell Therapy
All cells produce exosomes, but the cell types we are dealing with are derived from mesenchymal stem cells (MSC) from which all internal organs in the body are derived. These MSC are progenitor cells which means that under the right circumstances, they can develop into the cells of the organ they developed from and even form complete organs.
During stem cell therapy, it was thought that injected cells migrated to the target organ and supported the healing process. However, it has since been discovered that the injected stem cell mainly accumulates in the lungs, liver and spleen where they survive for about 3-7 days and produces a large amount of stem cell specific exosomes.
The newly produced exosomes remain functional for up to a month during which time they can enter local stem cells (for example the resident local stem cells in the synovial capsule of the knee) and induce new protein production that results in more identical exosomes being produced. In that way, the exosome message is cascaded into a large number of cells and reduces for example the inflammatory response or greatly improves growth characteristics.
Generally, mesenchymal stem cells are typically sitting on the blood vessels as pericytes and function as a conductor of all the body cells, controlling their growth. Their position makes it easy for exosomes to enter the circulation and transmit their message to distant stem cells.
The exosomes from mesenchymal stem cells carry the same cell membrane receptors as the parent cells, and it is therefore highly likely that they accumulate at the inflammation/trauma site by receptor-medicated action.
Exosomes Used for Infertility Treatment Studies
The exosomes used are available commercially and have been obtained from non-embryonic placental mesenchymal stem cells that have been harvested from donated placental tissue. Prior to donating the placenta, the donor has been extensively tested for infectious diseases using the FDA-mandated donor infectious disease panels. She has also undergone comprehensive genetic testing. All test results must be normal, and the donation must be found appropriate.
- Exosomes can be preserved very well at -20°C for over 6 months, they are very easy to transport and can be administered immediately after thawing.
- Placental mesenchymal stem cells are extracted and grown in conditioned media under low O2 tension with growth factors to stimulate the exosome production.
- The cells and cell debris are then destroyed and removed by gradient centrifugation, the fluid sterile filtered, and exosomes concentrated in the sediment using ultracentrifugation at >100,000 g.
- Protein concentration is adjusted to 15 mg per 5 ml vial which corresponds to approximately one billion exosomes and then suspended in 0.9 % saline.
- The exosome content of growth factors, anti-inflammatory and immuno-modulatory substances is then determined before the exosomes are released.
The exosomes release the same factors that are secreted from stem cells, but they function during a much longer time period than stem cells. The use of exosomes avoids the stem cell harvesting procedure, and no cell enrichment or isolation procedure is necessary for the stem cells.
The Importance of Using Young Stem Cell Exosomes
The fact that the exosomes used in these studies are obtained from placental cells (young cells) ensures a good quality exosome production. Older cells reduce the exosome production by up to 70-80%, and the young stem cell exosomes are aimed at the production of growth factors and immuno-modulatory substances. In contrast, older cells are more prone to produce anti-inflammatory and anti-neoplastic substances.
As cells begin to grow older, DNA molecules get blocked and stop functioning. To get them to function again, methyl groups are added to lysine of the DNA histones. That opens up the DNA so that the gene can start to function again and express growth stimulating factors.
The gene functions for a while before the methyl groups get closed and it stops functioning. This is analogous to the fact that when we are young, we need growth factor to grow taller and bigger. Then, when we finish the growth spurt, anti-inflammatory factors are needed for our wellbeing.
Factors in the exosomes are capable to induce the methylation in the DNA and start a new activation of the gene. Young cells also do not produce tumorigenic factors that sometimes may occur in older cells.
Clinical Applications of MSC and Exosomes
MSC are potent producers for exosomes. Both MSC and exosomes derived from MSC have been used for several years to combat inflammatory conditions such as joint arthritis. Over the years, multiple new applications have emerged such as treatment for multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, autoimmune diseases, dermatological diseases and many other conditions.
At Friberg Fertility, we are now introducing exosomes in the treatment of a number of clinical problems encountered in gynecology and infertility. Learn more here.