Synthetic medicine
Vsevolod Belousov, Post-science
Before we talk about synthetic medicine, we need to talk about synthetic biology. This is a new term, but already well-established in science. People who follow the latest advances in biology and biomedical science may have noticed that all the good things that have happened in this area recently have happened just in the field of knowledge, which can be called "synthetic biology". Synthesis here is not a concept of chemical synthesis, but rather a philosophical concept, namely, obtaining new systems, in this case alive, with new properties from those that were not combined with each other before. That is, the creation of a new one from what existed before, but in other combinations.
A typical example of synthetic biology is optogenetics, when we take light–sensitive molecules, for example, from unicellular algae or from bacteria - antenna proteins that capture light. A current of ions passes through them under the influence of light, and if we embed such proteins into mouse neurons, we can use light to control the activity of rodent neurons. That is, we got a light-sensitive nervous system. Another example is CRISPR/Cas systems, which are components of bacterial immunity. We take this system, transfer it to eukaryotic cells and get genome editing – we control the places where you can cut the genome, and then integrate new genetic information there.
Another example is fluorescent proteins and biosensors, when we take the fluorescent protein of jellyfish or corals, embed it in eukaryotic or prokaryotic cells, in any living systems. This allows us to monitor the processes that take place there under a microscope. In the case of biosensors, we take some other protein to the fluorescent protein that can change its conformation, that is, its shape, in response to a stimulus. By stitching them together at the gene level, we get a protein that changes fluorescence in response to a stimulus.
These are all examples when we actually rearrange the genetic information about a protein from one system to another and get a living system with new properties that allows us to explore processes in a way we didn't know how to do before: control the activity of neurons, cut DNA and edit information. It all started with fluorescent proteins. This was the first field that revolutionized biomedical research. The fluorescent protein itself – green fluorescent protein (GFP) – was discovered in the 1960s, but was not used in any way because we did not know about its genetic information. But then a gene for a green fluorescent protein was found and then transferred to other living organisms. We made them glow, thereby learning to observe the processes in living systems by fluorescence. Biosensors were a kind of complication of this topic.
In our country, synthetic biology began from the moment when Russian biologist Sergey Anatolyevich Lukyanov went to a pet store, bought corals and the genes of red fluorescent proteins were cloned from them. At that moment, multicolored labeling of cells and monitoring of parameters in them became available. In our research, we actively use synthetic biology – both for the construction of biosensors and for controlling activity in cells. I have already talked about optogenetics. It has a number of disadvantages that hinder its practical application, including in biomedical technologies. When optogenetics appeared, there was great hope that now we will learn not only to control the behavior or memory of the mouse, but also to correct human pathologies. One of the disadvantages of this technology, which prevents it from being applied to humans, is blue or generally visible light, which is used to activate photosensitive antennas. Light penetrates poorly through living tissue. To activate a neuron in the depths of a human or animal brain, you will still have to implant an optical fiber.
The second disadvantage is the relatively low conductivity. That is, the current through one photosensitive ion channel is quite small. You have to shine a pretty strong blue light to activate the neuron. And strong lighting damages the fabric. The main limitation of optogenetics in medicine is that our immune system necessarily sooner or later recognizes cells carrying a foreign protein. It will attack them, produce antibodies and eventually destroy the tissue. Therefore, we are developing an alternative strategy that will circumvent these disadvantages by using temperature-sensitive, temperature-dependent channels rather than photosensitive ion channels.
When we touch something warm or cold, we feel it precisely because we have thermosensitive antennas located on our membranes in sensory neurons. They can be activated not only by temperature. Each of them also has a chemical molecule that can activate them. For example, in hot pepper there is a substance capsaicin – it is an activator of chemical channels that feel heat, so you have a false burning sensation. Many animal species have such sensory molecules. In experiments, we take them from snakes. Many snakes, for example, rattlesnakes, muzzles, belonging to the yamkogolov, have an organ on the muzzle – a fossa, which is a thermal imager. There are sensory neurons that capture heat.
We took channels from snakes and learned how to control the activity of mouse or danio fish neurons by integrating thermosensitive channels into them. This is such a large, complex project in which we cooperate, including with physicists, with the group of Alexey Zheltikov from Moscow State University, which creates photonics tools for us in order to irradiate cells with infrared lasers. With this technology, we have already learned how to control the activity of neurons. The main ion passing through the thermosensitive channel is calcium, which is a universal messenger ion in all cells of the human body. Through it, the cell function is often realized. For example, you have a beta cell of the pancreas that secretes insulin in response to the rise of glucose in the blood. The key event in a beta cell that leads to the release of insulin is an increase in the concentration of calcium in the cytosol of this cell. By integrating ion thermosensitive channels from snakes into the beta cell, we can control the activity of cells by laser radiation or any other method of heat delivery, and with the help of biosensors observe how the concentration of calcium ion inside the cell increases, decreases or changes.
All these methods have direct therapeutic applications, which we are now beginning to develop. For example, we can endow not only our sensory neurons with the property of thermosensitivity, but also some cells in other organs, that is, any cells that have a non-neuronal nature. Unlike the situation with bacterial or algal opsins, these cells will not be attacked by the immune system, because the proteins that we will use for therapy are our proteins. The immune system is trained not to see them and not to react to them. This is one of the promising, in our opinion, areas that we are currently working on in the laboratory.
There is a large area in synthetic medicine that is still connected with optogenetics – the restoration of vision. In many diseases associated with the degradation of the retina, retinal photoreceptors, optogenetics can still be used. The immune system does not "walk" into the eye – it is an immune privileged zone. The body believes that once the eye is closed by the vitreous body, then infection should not get there, so the immune system has nothing to do there. Now in the advanced phases of clinical trials there are technologies based on optogenetics, when the patient's rods, cones, retinal cells have degraded, but there are several layers of neurons that normally collect information from rods and cones and take it to the optic nerve and brain. There is an idea, successfully implemented, using viral delivery systems to integrate photosensitive proteins from algae into these cells and make these cells photosensitive, photosensitive. After that, patients gain vision. Of course, not as good as normal vision, but, apparently, it allows you to distinguish large details, chiaroscuro, patterns. A person can navigate in space based on these stimuli. It is difficult to take this technology further than the eyes, because the immune system attacks foreign elements.
Other components of synthetic medicine, the same biosensors, cannot be integrated directly into a person. But with their help, it is possible to observe the processes occurring in living systems, in cell culture, organoids, in a mouse, which can be a model of pathology. Subsequently, using the same systems, it is possible to search for or screen chemicals, potential drugs that affect this process. For example, we have a molecule of hydrogen peroxide, which, on the one hand, is a signaling molecule in the cell, and on the other hand, in pathological conditions, its increased concentration can cause oxidative stress. By creating a biosensor for hydrogen peroxide, we can observe how it changes in living systems in pathological contexts. Also, using the same biosensor, to search for chemical molecules that can reduce its concentration or, conversely, increase it, to do this in specific compartments or subcompartments of cells. This is possible, since the biosensor is a protein molecule, we can attach an intracellular localization signal to it, which will tell the cellular protein sorting machine: "Deliver this protein to the mitochondria" or "Send this protein to the nucleus." Thus, we will have a fluorescent protein or biosensor not just in the cell, but at a specific point in the cell where, as we assume, the pathological process takes place.
Some of the technologies of synthetic biology can, for example, thermogenetics, go directly into synthetic medicine and be used as a method of therapy. And there are technologies, such as fluorescent proteins and biosensors, that can be used indirectly to study pathological processes and their possible correction. Genome editing technologies should be mentioned separately, because this is also synthetic biology. Now a large number of clinical trials are being conducted on editing the genome of somatic cells, when it is not necessary to correct the whole body, but there are, for example, individual muscle cells in which, as a result of genetic protein breakdown, the function of muscle contraction is not normally realized. By delivering CRISPR/Cas genome editing systems to these cells with the help of viral systems, we can change these genes and restore muscle function. Another option is the recently sensational case of editing the genome of twins in China, when the genetic information of the whole organism changes directly at the stage of early embryogenesis. It is possible to change a gene in the whole organism, because it will then be soldered into the genome forever. In this case, many ethical questions arise. However, it is clear that in countries such as China, where the concept of ethics in culture is completely different than, for example, in the USA or Europe, and the criteria are softer and more vague, these technologies will develop whether we want it or not. This is the place where synthetic biology enters medicine most rapidly.
About the author:
Vsevolod Belousov – Doctor of Biological Sciences, Professor of the Russian Academy of Sciences, Head of the Laboratory of Molecular Technologies of the IBH RAS.
Portal "Eternal youth" http://vechnayamolodost.ru