ORCID: 0000-0003-0769-559X
The Quest for Immortality
The quest for immortality has been with us since the beginning of the human race. Until recently, however, it was the domain of philosophers, juju men, alche-mists and of course various con men. The proverbial Holy Grail, the Philosopher’s Stone, immortality potions or other magical spells were supposed to grant us this revered status of immortality. But all this has changed with the arrival of modern molecular biology. The quest for immortality has left the realm of science fi ction, religion and fairy tales. It has entered the reality as we know it. In this brief essay I will summarize the arguments supporting this, by any standard, bold claim.
The progress of biomedical research in the 21st Century has been amazing and there is no end in sight. One of the immediate consequences of that progress has been our better understanding of the functioning of the human body. This, in turn, led to an improved understanding of the molecular basis of diseases, allowing for easier or more precise interference with pathological processes. The consequences of this evolution in treatment are very interesting because they allow us to imagine a situation in which the curability of diseases will reach 100%. Several centuries ago, the average life expectancy was about 30 years. This has steadily improved and in developed countries in the fi rst half of the 20th century, life expectancy reached around 45 years. 100 years later it approaches 80 years, which is twice as much [Oeppen J., Vaupel J.W., 2002]. What does this mean? One way to interpret this observation is that in the last 100 years we managed to extend our life expect-ancy by 100%. And while one may argue about all the possible reasons for that, the dominant one is the progress of medicine and biomedical science. Thanks to the achievements of molecular biology and biomedicine, we are able to heal bet-ter and thus live longer. But do we, nonetheless, have a personal expiration date? Currently yes, but one can easily imagine a situation when we have been cured of every disease, including aging. The consequence will be very simple. We will have no objective reason to die and science will usher us into our Shangri-La.
For the remainder of this essay, I will focus on the technology of immortality. The game changer in biomedical research was the launch of the Human Genome Project [Venter J.C. et al., 2001; Lander E.S. et al., 2001]. The goal, which seemed
impossible at the time, turned out to be the most important molecular event in his-tory. It costed over a billion dollars and took 13 years to complete, yet it was worth every penny and every second invested. The project has provided many interesting observations. First of all, it addressed the most pertinent question at the time – how many genes it takes to make us, humans. The hypothesis was that since we are the so-called pinnacle of evolution, there should be hundreds of thousands of genes needed to make us, we are after all more complex than fruit fl ies… Well, the project was a reality check. While the fruit fl y has about 15,000 protein coding genes, hu-mans have about 20,000–25,000, the same as mice and other higher vertebrates and a few thousand less than zebrafi sh (Danio rerio), not hundreds of thousands as one might have wished [Nobrega M.A., Pennacchio L.A., 2004]. More seriously however, The Project resulted several very important developments. Scientifi cally, it uncovered many novel genetic relationships between diseases and DNA muta-tions. Technologically, it made its mark in two areas. One was the development of novel sequencing technologies called collectively The Next Generation Sequenc-ing (NGS). The second one was the birth of very sophisticated bioinformatics and Big Data Analysis tools to deal with the deluge of genomic information.
Routine sequencing began in the 1980s at the optimistic rate of about 400 DNA bases per week. Today, using NGS strategies, the entire human genome (3,500,000,000 bases) can be sequenced in a few days. The immediate conse-quence of this is that many thousands of human genomes have been seconse-quenced to date and the number is exponentially increasing. Why is this so important in our search for immortality? A thorough analysis of these data revealed many interest-ing thinterest-ings. For example, it has been shown that small genetic changes sometimes make us more resistant or less resistant to various diseases, and this knowledge is instrumental for both the diagnosis and the proposed treatment. The sequencing of human genomes and those of other animals revealed another interesting fact. Genes encoding proteins are very similar, if not identical, across species. So why do we not look like mice? This is due to the fact that these protein encoding genes take up about 2% of our genome and the rest is taken up largely by the regula-tory sequences. They govern the timing, location and intensity of gene expression leading to phenotypic differences across species, but also among humans. Any two humans may differ genomically by about 0.1%; not much, until one realizes that this is a difference in 3,500,000 bases… enough to look very different from one another. Thus, the regulation of gene expression is so important and studies of that regulation are now in the spotlight. This regulation is responsible for the fact that while every cell in the body has the same genetic composition, it will express a different set of genes in the form of RNA, later translated into corresponding proteins. The RNA content of the cell is called a transcriptome and this is where most of the NGS effort is currently directed. Of course, the current technologies permit going further to investigate the protein composition, metabolic changes et the cellular level etc. What once was called “genetics” became “genomics” (DNA mutations), transcriptomics” (RNA composition), proteomics” (protein composi-tion) or “omics” in general. These technologies open many doors, some of them we did not know, existed.
For instance, let’s focus on something simple, investigations into genes that are turned off or on in various diseases. The procedure is relatively simple: tran-scriptomes of healthy and sick cells are compared using NGS. Then the genes are grouped according to the function of the proteins they encode and assigned to vari-ous biological processes, for example, the process of excessive division in the case of cancer cell genes etc. While initially one could study these events at the level of tissue samples (for instance tissue biopsies), today it is possible to do it at the level of individual cells. This is crucial in monitoring for instance the shrinkage of a tumor during chemotherapy where the analysis of the individual cells reveals if all tumor cells respond to the treatment or only a part, risking the recurrence of the cancer. This information may then be used to adapt the strategy to design a more effi cient therapy, thereby extending patient’s life.
Cell research is needed but not suffi cient on the quest for immortality. To un-derstand the disease process better, its molecular processes need to be investigated using model organisms. Here the question arises whether it really makes sense to use a mouse, fi sh, chicken or fruit fl y. In other words, how much of mouse, chicken or fruit fl y is in “us”? It turns out that there is much more than commonly thought. There are two reasons for this: evolutionary and developmental. Evolution, build-ing incrementally on a once randomly created template, includes all prior genetic history. Thus, the genome of the fruit fl y was a template for the ensuing genomes leading eventually to fi sh, to land animals, primates and humans. This notion is very strongly supported by the accumulated genomic research. For instance, we share more than 70 percent of protein coding information with zebrafi sh and pro-gressively more so with birds, mice, monkeys etc. Nature is lazy and once it in-vents something, it will go out of its way not to redo it, but rather recycle the old ideas. This means that signaling cascades and networks, once in place, have not been signifi cantly changed over the evolutionary journey. Therefore, this molecu-lar conservation allows us to study events taking place in the human body by using animal proxies. From the biomedical point of view, this is very important since we can study a chosen molecular event in organisms other than humans and still receive disease-relevant information.
This was evolution, but what about development? One way to characterize embryonic development is to divide it into three stages. The fi rst one where the actual induction of embryogenesis takes place, gastrulation, is very diverse in different animals. After the gastrulation stage comes the so-called phylotypic stage, where all embryos look approximately the same. This was very nicely il-lustrated by a German embryologist Haeckel. At the end of the 19th Century he produced the famous drawing comparing the embryonic development of several species from fi sh to human. The key conclusion of that work was that at this developmental stage the embryos of a fi sh, chicken or human look basically the same. Later, at the adaptive stage, there is a large phenotypic variability allow-ing fi sh to swim in the water, birds to fl y etc. This “hourglass” model supports the notion that that since embryos from different species look the same at the phylotypic stage, most likely the same genes, signaling cascades and networks are involved in a species – independent way [Irie N., Kuratani S., 2014]. This
hy-pothesis has been experimentally proven many times over, and became important in biomedical research.
One of the biomedical paradigms puts forward that disease processes are partial-ly caused by the misregulation of the genes principalpartial-ly involved in developmental processes. This is partially linked to the “recycling hypothesis”: after all we have only about 20,000–25,000 genes to choose from. The same genes, but in different confi gurations, are responsible for hear, kidney or bone development. Consequent-ly, it should not be surprising that genes or entire networks that are important dur-ing development, very often function in disease processes. Thus, understanddur-ing the mechanism of their action, e.g. in fi sh, provides us with very valuable information on the function of this gene in human disease. While there is no ideal animal proxy for human diseases, selected model organisms offer different advantages. The ad-vantage of zebrafi sh is that within 24 hours after fertilization, the embryo develops all the most important organs such as eyes, beating heart, etc. The other advantages of zebrafi sh are transparency and ease of genetic modifi cation. Moreover, after introducing appropriate genetic modifi cations, the fi sh can be fl uorescently labeled in various ways; for example, it fl uoresces depending on developmental or disease processes that take place in it. Fish became a very popular model in neuroscience, cardiovascular and metabolic research. Fish can become fat on a high cholesterol diet, get a stroke, heart attack, epilepsy, autism etc. For example, one feature of autism is the lack of causative memory. This can be demonstrated experimentally where the fi sh can choose between two chambers, one light and one dark. In the latter, the fi sh will be treated with a slight electric shock. A normal fi sh learns very quickly and only enters the bright chamber. The autistic fi sh, for instance gener-ated by introducing autism-linked mutation in humans, cannot remember it and will continue to fl ow into the dark chamber with the same frequency. The versatil-ity of the model has been embraced by the Biopharmaceutical industry as well. There, the “sick” fi sh are used to screen for new pharmacological solutions to health problems. What is crucial is that this research can be done on a large scale, where dozens, hundreds and even thousands of different variants of the medicine can be tested on individual embryos to fi nd the most effi cient one. It is also a very good model to study cancer, not only because you can induce the cancer process in the fi sh but also implant human cancer cells into it. Once implanted, they behave the same in the fi sh as in humans when it comes to proliferation, gene expression or metastasis. Thus, the model based on zebrafi sh allows one to conduct research on a very wide range of topics concerning human diseases such as metabolomics, mitochondrial metabolism and angiogenesis [Bradford Y.M. et al., 2017].
Another very popular model organism is the mouse, used as a model organism since the end of the 19th century. Initially, by using classical genetics at the begin-ning of the 20th century, mice were used to study the consequences of mutations and gene function in a complex organism. Today, using various types of molecular technologies, one can insert genes into the mouse, remove them, turn them on when and where desired, and regulate the intensity of their expression. One can even replace the mouse genes with human ones, “humanizing the mouse” in the process. The “gene games” also allow one to label the entire cell populations in
mice and follow their behavior under a disease condition, which is especially rel-evant in neurological disorders. Importantly, all these observations can be carried out in vivo. In fact, the technology has gone so far that animal sacrifi ce has been signifi cantly reduced and the disease processes and treatment results can be visu-alized, live, on the same mouse. At present, in mice one can see basically exactly the same as in humans. So, in addition to normal X-rays, one can do magnetic resonance imaging or computed tomography. It is also possible to observe what happens in mice in real time at several cell resolutions, for example, with tumor metastases. This is very important because it allows very dynamic tracking of tu-mor development and response to pharmacological therapies.
Although mice are not people, there are quite a few genetic models of human diseases in mice, where the same gene mutated in humans and in mice gives the same, or a very similar, phenotype [Cacheiro P. et al., 2019]. Waardenburg syn-drome is caused by a mutation of the Pax3 gene and in humans causes, among other symptoms, a white spot on the forehead and a white spot on the lower abdo-men. Interestingly, the mice carrying this mutation look exactly the same and have the same developmental problems. Cranio-clavicular dysplasia is another example of where a defect in the same gene in mice and humans causes the same phenotype. There are many other examples where mice are very similar to humans. When it comes to neurological research, many human conditions such as epilepsy, autism, schizophrenia or Alzheimer’s disease are also modeled in mice. This organism therefore allows for in-depth study of molecular mechanisms and the search for new pharmacological solutions to treat or alleviate these diseases.
The latest achievement in the immortality quest is the work focusing on stem cells. Although they were discovered a long time ago, they attracted attention rela-tively recently because of new technologies that allow to use them to their full poten-tial. Stem cells come in different fl avors but have one common feature; they can be programmed to turn into any type of cell, any organ, any part of the human body if one directs these cells appropriately [Liu G., et al., 2020]. The stem cells are defi ned by their origin. Embryonic stem cells, which are currently the most effi cient, come from embryos at a very early stage of development – before gastrulation – and have the greatest potential for differentiation. Adult stem cells, currently used in the clinic, come from reservoirs that have been found in adult organisms. In fact, every type of tissue appears to have a corresponding stem cell niche; adipose, bone, muscle, brain, etc. For example, so-called muscle satellite cells have been found in the muscles and they can differentiate into muscle cells if the muscle is damaged. The third type of stem cell reservoir was discovered several years ago and this work was honored by the Nobel Prize to Shinya Yamanaka. Specifi cally, it was given for the discovery of the process in which skin cells can be turned back into stem cells, called induced pluripotent stem cells. They present a very interesting clinical solution because they can be obtained easier, have more therapeutic possibilities than adult stem cells and no ethical concerns specifi c for the embryonic stem cells [Yamanaka S., 2012].
Practical applications of stem cell technologies are entering daily life. In the laboratory, they are used to restore missing hair on the mouse’s head, produce new teeth or repair the intestines. In humans, they are already used to repair the heart
after a heart attack, bone defects, spinal cord injury etc. Stem cells are also very effectively used to repair cartilage in human joints that have been damaged by osteoarthritis. Even more interestingly, at least in the laboratory, they can be used to rebuild a functional eye, liver, part of the lungs, and, very importantly, one can reconstruct the pancreas, which in turn is vital in the treatment of diabetes.
There are interesting consequences of the stem cell work. One of them relates to cancer because it enables two therapeutic approaches. In one strategy, patient stem cells can be isolated, genetically modifi ed and used to repair defects in the same patient. In the second, especially important in the treatment of cancer, the stem cells from the patient are collected to test various medications outside the patient’s body. The advantage of this strategy is that the patient is not exposed to chemotherapy and the drug that works can go back to the patient reducing the side effects of the therapy.
Here I would like to return to the thesis that we are on the road to immortality. Currently, when faced with an organ failure, one can make a new one. It is impor-tant to stress, however, that soon we will be able to rebuild more. In fact, we will be able to keep on repairing ourselves forever as we get older. Should that fail, we will be able to recreate ourselves by cloning. The fi rst cloning of the frog was carried out in the late fi fties of the last century by John Gurdon who got together with Shinya Yamanaka the Nobel Prize. Then came the famous Dolly the sheep, and now dogs or cats or in fact any vertebrate can be cloned. For about 40,000 dollars today one can clone one’s favorite cat or dog, as Barbara Streisand did. So what about human cloning, moral and ethical problems notwithstanding? While you should never say never, the current obstacles to choosing such a solution are at least two. First of all, the procedure is complicated and therefore very ineffi cient, for now at least. As we know, the technology moves forward and this is rather an issue of time. Secondly, even if the human body could be cloned, we remain with the unsolved problem of memory.
We are what we remember and if we clone ourselves, the clone will not have our memory, it will not be “I” we are looking for. No? Well…., biomedicine to the rescue. There are several reports on memory cloning in snails but also in mice. In the case of snails, the animals were conditioned to “learn” a new refl ex (yes, you can teach snails tricks), the RNA was isolated from selected brain cells and injected into recipient snails. Intriguingly, theses snails “knew” how to react [Chen S. et al., 2014]. Memory from one snail was cloned into another. In the case of mice, using a technique called “optogenetics” it was possible to implant nonexistent memories into mouse’s brain [Vetere G. et al., 2019]. So, one can see what the next likely step might be. Memory cloning, computer back up of consciousness? And why not? Enter “engrams”, defi ned as a singular memory, a physical change in brain tis-sue containing one recollection [Tonegawa S. et al., 2015]. Hogwart’s “pensieve” as a reality. The concept of cloning the memory, storing it and passing it onto the clone is becoming more real.
So, we are standing on the threshold of the Brave New World where immortal-ity becomes achievable. Because if a disease will not kill us, then what will? The old age is just another disease, after all…
Bibliography
Bradford Y.M., Toro S., Ramachandran S., Ruzicka L., Howe D.G., Eagle A., et al.,
Ze-brafi sh Models of Human Disease: Gaining Insight into Human Disease at ZFIN,
„ILAR J.” 2017;58(1):4–16.
Cacheiro P., Haendel M.A., Smedley D., International Mouse Phenotyping C, the
Mon-arch I. New models for human disease from the International Mouse Phenotyping Consortium, „Mammalian genome: offi cial journal of the International Mammalian
Genome Society” 2019;30(5–6):143–50.
Chen S., Cai D., Pearce K., Sun P.Y., Roberts A.C., Glanzman D.L., Reinstatement of
long-term memory following erasure of its behavioral and synaptic expression in Ap-lysia, „eLife” 2014;3:e03896.
Irie N., Kuratani S., The developmental hourglass model: a predictor of the basic body
plan? „Development” 2014;141(24):4649–55.
Lander E.S., Linton L.M., Birren B., Nusbaum C., Zody M.C., Baldwin J., et al., Initial
sequencing and analysis of the human genome, „Nature” 2001;409(6822):860–921.
Liu G., David B.T., Trawczynski M., Fessler R.G, Advances in Pluripotent Stem Cells:
History, Mechanisms, Technologies, and Applications, „Stem Cell Rev Rep.”
2020;16(1):3–32.
Nobrega M.A., Pennacchio L.A., Comparative genomic analysis as a tool for biological
discovery, „The Journal of physiology” 2004;554(Pt 1):31–9.
Oeppen J., Vaupel J.W., Demography. Broken limits to life expectancy, „Science” 2002;296(5570):1029–31.
Tonegawa S., Liu X., Ramirez S., Redondo R., Memory Engram Cells Have Come of Age, „Neuron” 2015;87(5):918–31.
Venter J.C., Adams M.D., Myers E.W., Li P.W., Mural R.J., Sutton G.G., et al, The
se-quence of the human genome, „Science” 2001;291(5507):1304–51.
Vetere G., Tran L.M., Moberg S., Steadman P.E., Restivo L., Morrison F.G., et al., Memory
formation in the absence of experience, „Nature neuroscience” 2019;22(6):933–40.
Yamanaka S., Induced pluripotent stem cells: past, present, and future, „Cell stem cell.” 2012;10(6):678–84.
Przemko Tylzanowski
Wyprawa po Nieśmiertelność
Streszczenie
Dążenie do nieśmiertelności towarzyszy nam od początku istnienia rasy ludzkiej. Do niedawna była to jednak domena fi lozofów, szamanów, al-chemików i oczywiście różnych oszustów. Przysłowiowy Święty Graal, Kamień Filozofi czny, eliksiry, woda życia lub inne magiczne zaklęcia miały nadać nam ten zaszczytny status nieśmiertelności. Wszystko zmieniło się wraz z nadejściem współczesnej biologii molekularnej. Dążenie do nieśmiertelności opuściło sferę science fi ction, religii i bajek. Weszła ona
w rzeczywistość taką, jaką znamy. Postępy w badaniach biomedycznych zostaną w tym eseju krótko omówione. Przedstawione zostaną argumenty na poparcie tezy, że nieśmiertelność jest bliższa niż nam się wydaje. Słowa kluczowe: nieśmiertelność, biomedycyna, genetyka, klonowanie
Przemko Tylzanowski
The Quest for Immortality
Abstract
The quest for immortality has been with us since the beginning of the human race. Until recently, however, it was the domain of philosophers, juju men, alchemists and of course various con men. The proverbial Holy Grail, the Philosopher’s Stone, immortality potions or other magical spells were sup-posed to grant us this revered status of immortality. But all this has changed with the arrival of modern molecular biology. The quest for immortality has left the realm of science fi ction, religion and fairy tales. It has entered the reality as we know it. The progress in biomedical research will be briefl y discussed. The arguments will be presented to support the notion that im-mortality is closer than we think.
