BiologicalBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
immortalityImmortality is the concept of living in a physical or spiritual form for an infinite or inconceivably vast length of time....
is the absence of a sustained increase in
rate of mortalityMortality rate is a measure of the number of deaths in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 in a population of 100,000 would mean 950 deaths per...
as a function of chronological age. A cell or organism that does not experience, or at some future point will cease,
agingSenescence refers to the biological changes which take place in organisms as they age. It encompasses all of the biological processes of a living organism's approaching an advanced age...
, is biologically immortal. However this definition of immortality was challenged in the new "Handbook of the Biology of Aging", because the increase in rate of mortality as a function of chronological age may be negligible at extremely
old ageOld age consists of ages nearing or surpassing the average life span of human beings, and thus the end of the human life cycle. Euphemisms and terms for old people include seniors , Senior Citizens , or the elderly...
s (late-life mortality plateau).
BiologicalBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
immortalityImmortality is the concept of living in a physical or spiritual form for an infinite or inconceivably vast length of time....
is the absence of a sustained increase in
rate of mortalityMortality rate is a measure of the number of deaths in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 in a population of 100,000 would mean 950 deaths per...
as a function of chronological age. A cell or organism that does not experience, or at some future point will cease,
agingSenescence refers to the biological changes which take place in organisms as they age. It encompasses all of the biological processes of a living organism's approaching an advanced age...
, is biologically immortal. However this definition of immortality was challenged in the new "Handbook of the Biology of Aging", because the increase in rate of mortality as a function of chronological age may be negligible at extremely
old ageOld age consists of ages nearing or surpassing the average life span of human beings, and thus the end of the human life cycle. Euphemisms and terms for old people include seniors , Senior Citizens , or the elderly...
s (late-life mortality plateau). But even though the rate of mortality ceases to increase in old age, those rates are very high (e.g., 50% chance of surviving another year at 110 or 115 years of age).
No actual
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
or individual
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
is inviolably
immortalImmortality is the concept of living in a physical or spiritual form for an infinite or inconceivably vast length of time....
(i.e. "invincible" or "indestructible"). Any real
livingLife is a characteristic that distinguishes objects that have self-sustaining biological processes from those that do not—either because such functions have ceased , or else because they lack such functions and are classified as "inanimate."In biology, the science of living organisms, "life"...
object enjoying
biological immortality can die upon receiving a sufficient injury or otherwise being killed or destroyed.
Cell lines
BiologistA biologist is a scientist devoted to and producing results in biology through the study of life.Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
s have chosen the word immortal to designate cells that are not limited by the
Hayflick limitThe Hayflick limit is the number of times a normal cell population will divide before it stops, presumably because the telomeres reach a critical length.-Overview:...
(where cells no longer divide because of
DNA damageDNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and Radiation can cause DNA damage, resulting in as many as 1...
or shortened
telomereA telomere is a region of repetitive DNA at the end of a chromosome, which protects the end of the chromosome from destruction. Its name is derived from the Greek nouns telos "end" and merοs "part"....
s). (Prior to the work of
Leonard HayflickLeonard Hayflick , Ph.D., is Professor of Anatomy at the University of California, San Francisco, School of Medicine, and was Professor of Medical Microbiology at Stanford University School of Medicine. He is a past president of the Gerontological Society of America and was a founding member of the...
there was the erroneous belief fostered by
Alexis CarrelAlexis Carrel was a French surgeon, biologist and eugenicist, who was awarded the Nobel Prize in Physiology or Medicine in 1912...
that all normal
somaticThe term somatic refers to cells of the body, rather than gametes . In humans, somatic cells contain two copies of each chromosome , whereas gametes only contain one copy of each chromosome...
cells are immortal.)
The term immortalization was first applied to
cancerCancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
cells that expressed the telomere-lengthening
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at...
telomeraseTelomerase is an enzyme that adds specific DNA sequence repeats to the 3' end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. The telomeres contain condensed DNA material, giving stability to the chromosomes...
, and thereby avoided
apoptosisApoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed cell death involves a series of biochemical events leading to a characteristic cell morphology and death; in more specific terms, a series of biochemical events that lead to a variety of...
(programmed cell death). Among the most commonly used cell lines are
HeLaA HeLa cell is an immortal cell line used in scientific research. The cell line was derived from cervical cancer cells taken from Henrietta Lacks, who died from her cancer on October 4, 1951....
and
JurkatJurkat cells are an immortalized line of T lymphocyte cells that are used to study acute T cell leukemia, T cell signaling, and the expression of various chemokine receptors susceptible to viral entry, particularly HIV. Jurkat cells are also useful in science because of their ability to produce...
, both of which are immortalized cancer cell lines. Normal
stem cellStem cells are cells found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian...
s and
germ cellGerm cells are progenitors of the gametes. These singled-out cells move through the gut to the developing gonads and undergo mitotic proliferation followed by meiosis and differentiation into either eggs or sperm . Plants do not have a germ line set aside in early development...
s can also be said to be immortal (when we refer to the cell line). The immortality of a single cell has never been observed.
Immortal cell lines of cancer cells can be created by induction of oncogenes or loss of
tumor suppressor geneA tumor suppressor gene, or antioncogene, is a gene that protects a cell from one step on the path to cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes.-Two-hit hypothesis:Unlike...
s. One way to induce immortality is through viral-mediated induction of the
large T-antigenSV40 large T antigen is a hexamer protein that is an oncogene derived from the polyomavirus SV40 which is capable of transforming a variety of cell types. The transforming activity of TAg is due in large part to its perturbation of the retinoblastoma and p53 tumor suppressor proteins...
, commonly introduced through
simian virus 40SV40 is an abbreviation for Simian vacuolating virus 40 or Simian virus 40, a polyomavirus that is found in both monkeys and humans...
(SV-40).
In terms of multi-cellular organisms, immortality may not be a desirable condition, as the main controls over cancer are the apoptotic mechanisms.
Bacteria
BacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
is said to be biologically immortal, but only as a
colonyIn biology, a colony refers to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defences or the ability to attack bigger prey. Some insects live only in colonies...
. An individual bacterium can easily die. The two daughter bacteria resulting from
cell divisionCell division is a process by which a cell, called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing...
of a parent bacterium can be regarded as unique individuals or as members of a
biologicallyBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
"immortal" colony. The two daughter cells can be regarded as "
rejuvenatedRejuvenation is the hypothetical reversal of the aging process.Rejuvenation is distinct from life extension. Life extension strategies often study the causes of aging and try to oppose those causes in order to slow aging...
" copies of the parent cell because damaged
macromoleculeA macromolecule is a very large molecule most often created by some form of polymerization. In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
s have been split between the two cells and diluted. In the same way stem cells and
gameteA gamete is a cell that fuses with another gamete during fertilization in organisms that reproduce sexually...
s can be regarded as "immortal".
Hydra
HydraHydra is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a...
s are a genus of simple, fresh-water animals possessing radial symmetry and no post-mitotic cells. The fact that all cells continually divide allows defects and toxins to be "diluted-away". It has been suggested that hydras do not undergo
senescenceSenescence refers to the biological changes which take place in organisms as they age. It encompasses all of the biological processes of a living organism's approaching an advanced age...
(aging), and so are biologically immortal. However, this does not explain how hydras are consequently able to maintain telomere lengths.
Jellyfish
Turritopsis nutriculaTurritopsis nutricula is a hydrozoan with a life cycle in which it reverts to the polyp stage after becoming sexually mature. It is the only known case of a metazoan capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary stage. It...
is a small (5mm) species of jellyfish which uses
transdifferentiationTransdifferentiation in biology takes place when a non-stem cell transforms into a different type of cell, or when an already differentiated stem cell creates cells outside its already established differentiation path. Developmental biologist and biochemist David Tosh has restricted the definition...
to become younger after sexual reproduction. This cycle can repeat indefinitely, rendering it biologically immortal. It originates from the Caribbean sea, but has now spread around the world.
Life extensionists
Some
life extensionLife extension, also known as anti-aging medicine, experimental gerontology, and biomedical gerontology, refers to attempts to slow down or reverse the processes of aging to extend both the maximum and average lifespan...
ists, such as those who practice
cryonicsCryonics is the low-temperature preservation of humans and animals that can no longer be sustained by contemporary medicine until resuscitation may be possible in the future. Currently, human cryopreservation is not reversible, which means that it is not currently possible to bring people out of...
, have the hope that humans may someday become biologically immortal. This would not be the same as literal
immortalityImmortality is the concept of living in a physical or spiritual form for an infinite or inconceivably vast length of time....
, since people are still susceptible to death through external circumstances (either deliberate or accidental). In other words, being biologically immortal doesn't mean one is invincible and is not still prone to physical damage, disease, and so on.
A study published in Physiological and Biochemical Zoology in 2005 suggests that a stage may exist in species generally, and has been observed in some where: “the exponential increase in age-specific death rate seemed to slow down considerably, if not cease,” a third phase after aging when the various challenges that the aging processes normally present are met and senescence is no longer a factor.
The biogerontologist
Aubrey de GreyAubrey David Nicholas Jasper de Grey is an English author and theoretician in the field of gerontology, and the Chief Science Officer of the SENS Foundation....
proposed that damage to
macromoleculeA macromolecule is a very large molecule most often created by some form of polymerization. In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
s,
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
s,
tissueTissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function...
s and
organIn biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function ....
s could be repaired by advanced
biotechnologyBiotechnology is technology based on biology, agriculture, food science, and medicine. Modern use of the term usually refers to genetic engineering as well as cell- and tissue culture technologies...
. He calls his project SENS (Strategies for Engineered Negligible Senescence). Dr. de Grey has created the Methuselah Mouse Prize to award money to researchers who can significantly extend the lifespan of, or
rejuvenateRejuvenation is the hypothetical reversal of the aging process.Rejuvenation is distinct from life extension. Life extension strategies often study the causes of aging and try to oppose those causes in order to slow aging...
mice. It is his hope that if a monetary reward is offered, it will increase the likelihood of mice being rendered extremely, unnaturally long-lived by science, and that such a feat will inspire research into replicating this achievement in humans which may spark a "
buy-in" with many people willing to pay large amounts of money for the benefits of such research.
See also
- DNA damage theory of aging
The DNA damage theory of aging proposes that aging is a consequence of unrepaired DNA damage accumulation. Damage in this context includes chemical reactions that mutate DNA and/or interfere with DNA replication. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear...
- Aging Research Centre
The Aging Research Centre is an independent non-profit educational research centre with facilities in Berkeley, California and in Waterloo, Ontario...
- American Academy of Anti-Aging Medicine
The American Academy of Anti-Aging Medicine is a United States registered 501 nonprofit organization that promotes what it calls "anti-aging medicine." The A4M was founded in 1993 by Robert Goldman and Ronald Klatz, who were trained as osteopathic physicians...
- Strategies for Engineered Negligible Senescence (SENS)
- Immortality Institute
The Immortality Institute is a nonprofit501 organization with the mission "to conquer the blight of involuntary death." The organization hosts an online forum, publishes books, creates films, and sponsors conferences in order to advance life extension research...
- Hayflick limit
The Hayflick limit is the number of times a normal cell population will divide before it stops, presumably because the telomeres reach a critical length.-Overview:...
- Hydra
Hydra is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a...
- Life extension
Life extension, also known as anti-aging medicine, experimental gerontology, and biomedical gerontology, refers to attempts to slow down or reverse the processes of aging to extend both the maximum and average lifespan...
- Maximum lifespan
- Methuselah Foundation
The Methuselah Foundation is a non-profit 501 volunteer organization co-founded by Aubrey de Grey and David Gobel, which is based in Springfield, Virginia, United States...
- Senescence
Senescence refers to the biological changes which take place in organisms as they age. It encompasses all of the biological processes of a living organism's approaching an advanced age...
- Reliability theory of aging and longevity
Reliability theory of aging and longevity is a scientific approach aimed to gain theoretical insights into mechanisms of biological aging and species survival patterns by applying a general theory of systems failure, known as reliability theory.-Overview:...
- Cryptobiosis
Cryptobiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and repair...
External links