The astrocytic hypothesis of aging of mammals
Encyclopedia
Radial glia
Radial glial cells are a pivotal cell type in the developing central nervous system involved in key developmental processes, from patterning and neuronal migration to their recently discovered role as precursors during neurogenesis. They arise early in development from neuroepithelial cells...
cells into star-shaped astrocytes during the postnatal development, i.e. disappearance of the fetal radial ways of neuroblasts migration from proliferative zones to the sites of their ultimate localization in the brain of adult individuals.
The astrocytic hypothesis was proposed by Ukrainian biologist
Biologist
A 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...
Olexiy Boyko in 2000, published in 2004, and in the final formulated in 2007 It is common among scholars who study the phenomenon of ageing
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
.
Prerequisites
The astrocytic hypothesis appeared during a systemic crisis in ageing biology and gerontologyGerontology
Gerontology is the study of the social, psychological and biological aspects of aging...
, when the old principles of conceptual models of ageing, which came to absolutisation of some phenomena and private mechanisms of ageing, are failed. In other words, it became clear that theories of ageing have no ability to predict on the background of how even
well known scientists offer a paradigm shift in aging biology.
More moderate views are thought by O.G. Boyko (the author of the astrocytic hypothesis) that the time of its appearance coincided with the completion of verification of most of ageing hypotheses, which directly link specific cellular processes with the initial cause of the ageing in the whole organism.
Their failure in this respect confirmed the existence of species of multicellular animals (Metazoa) with negligible senescence
Negligible senescence
Negligible senescence refers to the failure of a few select animals to display symptoms of aging. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly...
(non ageing), that do not preclude any generation of reactive oxygen species or shortening of telomere
Telomere
A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...
s, apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
and other cellular processes, which typically account for ageing. This fact is not surprising, as pools of cellular mechanisms in both ageing species and ageless species of Metazoa virtually indistinguishable. Also rejected the traditional view that mortal genes (ageing
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
and death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
) appeared simultaneously with the appearance Metazoa and distribution functions between tissues, as are details about the existence of not only the species of multicellular animals Metazoa with negligible senescence
Negligible senescence
Negligible senescence refers to the failure of a few select animals to display symptoms of aging. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly...
, but also potentially immortal species of Metazoa. A good example is an individual of Antarctic sponges Scolymastra joubini
Hexactinellid
Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges...
, whose estimated age is from 15 to 23 thousand years
. Finding of the root causes of ageing it has moved from cell level to organism level. Researchers have begun to compare the evolutionary design (species-specific features of anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, morphology
Morphology
Morphology may mean:*Morphology , the study of the structure and content of word forms*Morphology , the study of the form or shape of an organism or part thereof...
, physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
, etc.) ageless, ageing slowly and rapidly ageing animals. One of the results of the search is the astrocytic hypothesis.
Contents of the astrocytic hypothesis
The astrocytic hypothesis is based on common knowledge that in vertebrates (Vertebrata) the place of generation neuroblastNeuroblast
A neuroblast is a dividing cell that will develop into neurons or glia. The characterisation of neuroblasts and their development in Drosophila melanogaster was widely achieved by Chris Doe, Corey Goodman and Mike Bate. In humans, neuroblasts produced by stem cells in the adult subventricular zone...
s in an adult as well as in embryonic phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
are separated from their final localization. If you bear in mind the adult phenotype, in this case neuroblasts are produced in ventricular / subventricular zone
Subventricular zone
The subventricular zone is a paired brain structure situated throughout the lateral walls of the lateral ventricles. It has been associated with having four distinct layers of variable thickness and cell density, as well as cellular composition....
where persisted neural stem cells into adulthood, and then migrate along fibers of radial glia on a long distance, that except for mammals.
At mammal during neurogenesis 80-90 % of neuron precursors in a brain migrate along radial glia fibers which represent as though clues of a direction of this migration. But as against those vertebrates at which neurogenesis at adult individuals it is observed, and radial glia cells are kept for life, at mammal after the period of neurons migration the radial glia cells are transformed in stellate astrocytes, except for hippocamp
Hippocamp
The hippocamp or hippocampus , often called a sea-horse in English, is a mythological creature shared by Phoenician and Greek mythology, though the name by which it is recognised is purely Greek; it became part of Etruscan mythology...
al dentate gyrus.
In other words, the disappearance of radial glia cells in the postnatal period of development prohibits physiological and reparative regeneration of nervous tissue. Therefore, “a postmitotic brain" where neurons are not updated pool for life is a unique phenomenon among vertebrates and specific only to mammals. Convincing data, especially Jonas Frisen and Ellen Heber-Katz
Ellen Heber-Katz
Ellen Heber-Katz is professor at the Wistar Institute in Philadelphia. She participated in the research of the Murphy Roths Large .- Education :* University of Wisconsin, Madison, WI B.A. 1969 Medical Microbiology...
again demonstrated that the mammalian body part that is not updated during the life is only nervous tissue (brain). Specifically neurons that are its building blocks.
The astrocytic hypothesis suggests that ageing of mammals is a genetic disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
that causes death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
. Its cause is acquiring in the evolution process of the theriomorph lineage of the vertebrates (aromorphosis): - radial glia cells transformation in stellate astrocyte
Astrocyte
Astrocytes , also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord...
s in the postnatal period of development, i.e. disappearance of embryonic radial migration of neurons from proliferative zones to places of their final localization in the adult brain.
The astrocytic hypothesis in popular-science literature and media
The astrocytic hypothesis described in popular-science form by Elena Naymark, Rosa Barsova and Cyril Hryschenkov, scientific observer of the magazine "7 days "(Moscow, Russia).In the media, and on its website astrocytic hypothesis promotes professionally by known Russian gerontologists Boris Kaurov. The appearance of the astrocytic hypothesis in the Journal of General Biology accompanied by publications in the media and scientific press. The article G.A. Tarasevich: - "We could live would be eternal. Only nerves prevented " argues that Boyko astrocytic hypothesis is actually an advanced version elevation hypothesis of ageing by Vladimir Dilman. With publications in the scholarly press attractive paper "Reason For Mammals' Aging Lies In The Brain", articles about the astrocytic hypothesis appeared in some encyclopedias.
Criticism
Moskalev A.A. (Institute of Biology, Komi Scientific Centre, Ural Branch, Russian) presents facts and arguments against the astrocytic hypothesis. In particular:A. A. Moskalev arguments should be interpreted two ways: on the one hand, they point to bottleneck problems of astrocytic hypothesis, on the other hand, they show incomplete database of modern biological science. In response to criticism O.G. Boyko suggested evolutionary study of the phenomenon of ageing combining astrocytic hypothesis with hypothesis of A. V. Makrushin. Such a combination, according to O.G. Boyko, rejects criticism A.A. Moskalev, who in turn met the emergence of a new doctrine of strong criticism, in particular, he writes: -
In general, A.A. Moskalev agrees with O.G. Boyko on what each evolutionary branch of live beings have inherent varying mechanisms of ageing, that is caused by the evolutionary design of phylogenetic group. In turn, with this point of view strongly disagree A.M. Olovnikov (the author of telomere-telomerase hypothesis of ageing), which in general repeated the arguments of A.A. Moskalev. A.M. Olovnikov assumes that ageing is performed in all species of Metazoa by the unknown molecular mechanism. In other words, that is not yet the discovered cellular mechanism.
Astrocytic hypothesis is discussed in reviews V.V. Zyuganov
Valeriy Zyuganov
Valeriy Valeryevich Zyuganov is a Soviet and Russian biologist, and Doctor of Biological Sciences. He is the pupil and follower of professors V.V. Khlebovich, and Yu. A...
, Aubrey de Grey
Aubrey de Grey
Aubrey 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. He is editor-in-chief of the academic journal Rejuvenation Research, author of The Mitochondrial Free Radical Theory of Aging and co-author...
, A.V. Khalyavkin, A.I. Yashin, I. Yu. Popov, A. N. Ostrovsky, and V. N. Anisimov.
The first experimental confirmation
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Summarizing the overall database in 2009 year (results of different authors from 1980’s of the last century to this day) author of the astrocytic hypothesis concluded that physiological regeneration in birds takes place in the entire volume of nervous tissue without restrictions. Restored not only the loss in a pool of neurons, the brain of birds is capable to the reparative regeneration of traumatic injury that was the unknown at the time of nomination astrocytic hypothesis in 2000–2004 years. This phenomenon owes its existence because as expected, kept a well-developed radial embryonal network in brain of adult birds that provides migration of newborn neurons (neuroblasts) with a common to all vertebrates, their place of birth - ventral / subventricular zones of the brain into the place of reparations or their final localization in the brain of adult individuals.
Soon after the final wording of the astrocytic hypothesis in 2007 appeared incontrovertible data that neuronal turnover in brain of birds, although in a very small extent, but still limited - after selective removal of several cell types of neurons, they do not regenerate.
Predicted hypothetical factor of the longevity of life in birds, that is a permanent updated pool of neurons nervous tissue, in turn should prevent the accumulation senescent hormone–synthesizing neurons and thus must be hinder the development of Dilman process, i.e. parameters of homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
adult birds must be kept for life on one level.
In 2010 Vincent Julien Lecomte at least for wandering albatross
Wandering Albatross
The Wandering Albatross, Snowy Albatross or White-winged Albatross, Diomedea exulans, is a large seabird from the family Diomedeidae, which has a circumpolar range in the Southern Ocean. It was the first species of albatross to be described, and was long considered the same species as the Tristan...
(Diomedea exulans) established the fact that in this bird important physiological parameters (markers of ageing) of homeostasis for life do not change, as stipulated by the astrocytic hypothesis.
Almost is not limited, but still partial turnover of the neurons pool in the nervous tissue of birds require an irreplaceable part of the pool, which undergoes to cellular ageing, which is apparently tolerated into the organism level, probably because Diomedea exulans getting older: there are unfavourable changes with age in the ability to foraging and reproductive function.
However, this conclusion is true for other species of birds. It is generally accepted that among birds there are no species with negligible ageing. This is true for mammals. However, the reparative potency of nervous tissue in birds with age, tend to decrease.
Value the astrocytic hypothesis with other hypothesis of ageing
In the PubMed database stored 164 567 articles devoted to the free-radical hypothesis of ageing, but they are very inconsistent. Therefore, this hypothesis has many supporters and opponents. The astrocytic hypothesis postulates a cascade of events and conditions under which, indeed, due to free-radical processes be can tear and wear of a multicellular organism. At least in mammals: - prohibition of physiological regeneration of nerve tissue (the neurons pool).The elevation hypothesis of V.M. Dilman (modern version - the neuroendocrine theory of ageing) connects the ageing changes of organism with hypothalamic sensitivity to regulatory signals from the nervous system and endocrine glands with ageing at the organism level. The neuroendocrine theory is not yet completed, since the primary cause of age-endocrine changes in this theory is undisclosed. The astrocytic hypothesis describes the initial cause of these changes and its evolutionary origin. In addition, the astrocytic hypothesis associated with the hypothesis of ageing by G.P. Bidder and denies the majority postulates of the phenoptosis
Phenoptosis
Phenoptosis signifies the phenomenon of programmed cell death of an organism, ie that an organism's biology includes features that under certain circumstances will cause it to rapidly degenerate and die off...
hypothesis by V. P. Skulachov. It should be noted that the biology of ageing is not generally accepted hypotheses. Assumed that schools support the postulates of their hypothesis of ageing. In aggregate, the hypothesis of ageing about 300.