Admin: 1 версия импортирована

2025-11-13T17:58:39Z

1 версия импортирована

← Предыдущая версия		Версия от 17:58, 13 ноября 2025
(нет различий)

ru>Rich Smith: v2.05 - Fix errors for CW project (Reference list duplication - ISSN with incorrect syntax - ISSN with wrong checksum)

2025-10-10T22:13:29Z

v2.05 - Fix errors for CW project (Reference list duplication - ISSN with incorrect syntax - ISSN with wrong checksum)

Новая страница

{{Short description|Limit to divisions of a normal human cell}}
The '''Hayflick limit''', or '''Hayflick phenomenon''', is the number of times a normal [[Somatic cell|somatic]], [[Cellular differentiation|differentiated]] human cell population will divide before [[cell division]] stops.<ref>{{Cite journal |last=Rodriguez-Brenes |first=Ignacio A. |last2=Wodarz |first2=Dominik |last3=Komarova |first3=Natalia L. |date=December 9, 2015 |title=Quantifying replicative senescence as a tumor suppressor pathway and a target for cancer therapy |journal=Scientific Reports |volume=5 |article-number=17660 |bibcode=2015NatSR...517660R |doi=10.1038/srep17660 |pmc=4673423 |pmid=26647820 |doi-access=free}}</ref><ref>{{Cite journal |last=Petersen |first=Thomas |last2=Niklason |first2=Laura |date=September 2007 |title=Cellular Lifespan and Regenerative Medicine |journal=Biomaterials |volume=28 |issue=26 |pages=3751–3756 |doi=10.1016/j.biomaterials.2007.05.012 |pmc=2706083 |pmid=17574669}}</ref>

The concept of the Hayflick limit was advanced by American anatomist [[Leonard Hayflick]] in 1961,<ref name="pmid13905659" /> at the [[Wistar Institute]] in [[Philadelphia]], Pennsylvania. Hayflick demonstrated that a normal [[human]] [[fetus|fetal]] cell population will divide between 40 and 60 times in [[cell culture]] before entering a [[Cellular senescence|senescence]] phase. This finding refuted the contention by [[Alexis Carrel]] that normal cells are [[biological immortality|immortal]].

Hayflick interpreted his discovery to be aging at the cellular level. The aging of cell populations appears to correlate with the overall physical aging of an organism.<ref name="pmid13905659">{{Cite journal |last=Hayflick L, Moorhead PS |year=1961 |title=The serial cultivation of human diploid cell strains |journal=Exp Cell Res |volume=25 |issue=3 |pages=585–621 |doi=10.1016/0014-4827(61)90192-6 |pmid=13905658}}</ref><ref name="pmid14315085">{{Cite journal |last=Hayflick L. |year=1965 |title=The limited in vitro lifetime of human diploid cell strains |journal=Exp. Cell Res. |volume=37 |issue=3 |pages=614–636 |doi=10.1016/0014-4827(65)90211-9 |pmid=14315085}}</ref>

[[Macfarlane Burnet]] coined the name "Hayflick limit" in his book ''Intrinsic Mutagenesis: A Genetic Approach to Ageing'', published in 1974.<ref name=Shay2000/>

== History ==
=== The belief in cell immortality ===
Prior to Leonard Hayflick's discovery, it was believed that [[vertebrate]] cells had an unlimited potential to replicate. [[Alexis Carrel]], a [[Nobel Prize]]-winning surgeon, had stated "that all cells explanted in [[tissue culture]] are immortal, and that the lack of continuous cell replication was due to ignorance on how best to cultivate the cells".<ref name=Shay2000/> He claimed to have cultivated [[fibroblasts]] from the hearts of [[chicken]]s (which typically live 5 to 10 years) and to have kept the culture growing for 34 years.<ref>{{Cite journal |last=Carrel A, Ebeling AH |year=1921 |title=Age and multiplication of fibroblasts |journal=J. Exp. Med. |volume=34 |issue=6 |pages=599–606 |doi=10.1084/jem.34.6.599 |pmc=2128071 |pmid=19868581}}</ref>

However, other scientists have been unable to replicate Carrel's results,<ref name="Shay2000" /> and they are suspected to be due to an error in experimental procedure. To provide required nutrients, [[embryonic stem cells]] of chickens may have been re-added to the culture daily. This would have easily allowed the cultivation of new, fresh cells in the culture, so there was not an infinite reproduction of the original cells.<ref name="pmid13905659" /> It has been speculated that Carrel knew about this error, but he never admitted it.<ref>{{Cite journal |last=Witkowski JA |year=1985 |title=The myth of cell immortality |journal=Trends Biochem. Sci. |volume=10 |issue=7 |pages=258–260 |doi=10.1016/0968-0004(85)90076-3}}</ref><ref>{{Cite journal |last=Witkowski JA |year=1980 |title=Dr. Carrel's immortal cells |journal=Med. Hist. |volume=24 |issue=2 |pages=129–142 |doi=10.1017/S0025727300040126 |pmc=1082700 |pmid=6990125}}</ref>

Also, it has been theorized{{By whom|date=February 2022}} that the cells Carrel used were young enough to contain [[cell potency|pluripotent stem cells]], which, if supplied with a supporting [[telomerase]]-activation nutrient, would have been capable of staving off replicative senescence, or even possibly reversing it. Cultures not containing telomerase-active pluripotent stem cells would have been populated with telomerase-inactive cells, which would have been subject to the 50 ± 10 mitosis event limit until [[cellular senescence]] occurs as described in Hayflick's findings.<ref name="pmid14315085" />

=== Experiment and discovery ===
Hayflick first became suspicious of Carrel's claims while working in a lab at the Wistar Institute. Hayflick noticed that one of his cultures of embryonic human [[fibroblasts]] had developed an unusual appearance and that cell division had slowed. Initially, he brushed this aside as an anomaly caused by contamination or technical error. However, he later observed other cell cultures exhibiting similar manifestations. Hayflick checked his research notebook and was surprised to find that the atypical cell cultures had all been cultured to approximately their 40th doubling while younger cultures never exhibited the same problems. Furthermore, conditions were similar between the younger and older cultures he observed—same culture medium, culture containers, and technician. This led him to doubt that the manifestations were due to contamination or technical error.<ref name="9780826129420-Hayflick">{{Cite book |last=Hayflick |first=L |title=Handbook of Theories of Aging |date=19 May 2016 |publisher=Springer Publishing Company |isbn=978-0-8261-2942-0 |editor-last=Bengtson |editor-first=VL |edition=Third |pages=31–52 |chapter=Unlike Aging, Longevity is Sexually Determined |editor-last2=Settersten |editor-first2=RA}}</ref>

Hayflick next set out to prove that the cessation of normal cell replicative capacity that he observed was not the result of viral contamination, poor culture conditions or some unknown artifact. Hayflick teamed with [[Paul Moorhead]] for the definitive experiment to eliminate these as causative factors. As a skilled [[cytogeneticist]], Moorhead was able to distinguish between male and female cells in culture. The experiment proceeded as follows: Hayflick mixed equal numbers of normal human male fibroblasts that had divided many times (cells at the 40th population doubling) with female fibroblasts that had divided fewer times (cells at the 15th population doubling). Unmixed cell populations were kept as controls. After 20 doublings of the mixed culture, only female cells remained. [[Cell division]] ceased in the unmixed control cultures at the anticipated times; when the male control culture stopped dividing, only female cells remained in the mixed culture. This suggested that technical errors or contaminating [[viruses]] were unlikely explanations as to why cell division ceased in the older cells, and proved that unless the virus or artifact could distinguish between male and female cells (which it could not) then the cessation of normal cell replication was governed by an internal counting mechanism.<ref name="pmid13905659" /><ref name="Shay2000">{{Cite journal |last=Shay |first=JW |last2=Wright |first2=WE |date=October 2000 |title=Hayflick, his limit, and cellular ageing. |journal=Nature Reviews Molecular Cell Biology |volume=1 |issue=1 |pages=72–6 |doi=10.1038/35036093 |pmid=11413492 |s2cid=6821048}}</ref><ref name="9780826129420-Hayflick" />

These results disproved Carrel's immortality claims and established the Hayflick limit as a credible biological theory. Unlike Carrel's experiment, Hayflick's have been successfully repeated by other scientists.{{cn|date=November 2024}}

== Cell phases ==
Hayflick describes three phases in the life of normal cultured cells. At the start of his experiment he named the primary culture "phase one". Phase two is defined as the period when cells are proliferating; Hayflick called this the time of "luxuriant growth". After months of doubling the cells eventually reach phase three, a phenomenon he named "[[Cellular senescence|senescence]]", where cell replication rate slows before halting altogether.{{cn|date=August 2023}}

== Telomere length ==
[[File:Hayflick Limit (1).svg|thumb|The typical normal human fetal cell will divide between 50 and 70 times before experiencing senescence. As the cell divides, the telomeres on the ends of chromosomes shorten. The Hayflick limit is the limit on cell replication imposed by the shortening of telomeres with each division. This end stage is known as [[cellular senescence]].]]

The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes. During the process of [[DNA replication]] of a chromosome, small segments of DNA within each [[telomere]] are unable to be copied and are lost.<ref>{{Cite journal |last=Watson JD |year=1972 |title=Origin of concatemeric T7 DNA |journal=Nature New Biology |volume=239 |issue=94 |pages=197–201 |doi=10.1038/newbio239197a0 |pmid=4507727}}</ref> This occurs due to the uneven nature of DNA replication, where leading and lagging strands are not replicated symmetrically.<ref>{{Cite journal |last=Rousseau |first=Philippe |last2=Autexier |first2=Chantal |date=October 2015 |title=Telomere biology: Rationale for diagnostics and therapeutics in cancer |journal=RNA Biology |language=en |volume=12 |issue=10 |pages=1078–1082 |doi=10.1080/15476286.2015.1081329 |pmc=4829327 |pmid=26291128}}</ref> The telomeric region of DNA does not code for any protein; it is simply a repeated code on the end region of linear eukaryotic chromosomes. After many divisions, the telomeres reach a critical length and the cell becomes senescent. It is at this point that a cell has reached its Hayflick limit.<ref>{{Cite journal |last=Olovnikov AM |year=1996 |title=Telomeres, telomerase and aging: Origin of the theory |journal=Exp. Gerontol. |volume=31 |issue=4 |pages=443–448 |doi=10.1016/0531-5565(96)00005-8 |pmid=9415101 |s2cid=26381790}}</ref><ref>{{Cite journal |last=Olovnikov |first=A. M. |year=1971 |title=Принцип маргинотомии в матричном синтезе полинуклеотидов |trans-title=Principles of marginotomy in template synthesis of polynucleotides |journal=[[Doklady Akademii Nauk SSSR]] |volume=201 |issue=6 |pages=1496–1499 |pmid=5158754}}</ref>

Hayflick was the first to report that only cancer cells are immortal. This could not have been demonstrated until he had demonstrated that normal cells are mortal.<ref name="pmid13905659" /><ref name="pmid14315085" /> [[Cellular senescence]] does not occur in most [[cancer cell]]s due to expression of an [[enzyme]] called [[telomerase]]. This enzyme extends telomeres, preventing the telomeres of cancer cells from shortening and giving them infinite replicative potential.<ref>{{Cite journal |last=Feng F |last2=Funk |first2=WD |last3=Wang |first3=SS |last4=Weinrich |first4=SL |last5=Avilion |first5=AA |last6=Chiu |first6=CP |last7=Adams |first7=RR |last8=Chang |first8=E |last9=Allsopp |first9=RC |display-authors=1 |year=1995 |title=The RNA component of human telomerase |journal=Science |volume=269 |issue=5228 |pages=1236–1241 |bibcode=1995Sci...269.1236F |doi=10.1126/science.7544491 |pmid=7544491 |s2cid=9440710}}</ref> A proposed [[experimental cancer treatment#Telomerase therapy|treatment for cancer]] is the usage of telomerase [[enzyme inhibitor|inhibitor]]s that would prevent the restoration of the telomere, allowing the cell to die like other body cells.<ref>{{Cite journal |last=Wright WE, Shay JW |year=2000 |title=Telomere dynamics in cancer progression and prevention: Fundamental differences in human and mouse telomere biology |journal=Nature Medicine |volume=6 |issue=8 |pages=849–851 |doi=10.1038/78592 |pmid=10932210 |s2cid=20339035}}</ref>

==Organismal aging==

Hayflick suggested that his results in which normal cells have a limited replicative capacity may have significance for understanding human aging at the cellular level.<ref name="pmid14315085" />

It has been reported that the limited replicative capability of human [[fibroblast]]s observed in [[cell culture]] is far greater than the number of replication events experienced by non-stem cells [[in vivo]] during a normal postnatal lifespan.<ref name="pmid9724752">{{Cite journal |vauthors=Cristofalo VJ, Allen RG, Pignolo RJ, Martin BG, Beck JC |year=1998 |title=Relationship between donor age and the replicative lifespan of human cells in culture: a reevaluation |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=95 |issue=18 |pages=10614–9 |bibcode=1998PNAS...9510614C |doi=10.1073/pnas.95.18.10614 |pmc=27943 |pmid=9724752 |doi-access=free}}</ref> In addition, it has been suggested that no inverse correlation exists between the replicative capacity of normal human cell strains and the age of the human donor from which the cells were derived, as previously argued. It is now clear that at least some of these variable results are attributable to the mosaicism of cell replication numbers at different body sites where cells were taken.<ref name="pmid9724752" />

Comparisons of different species indicate that cellular replicative capacity may correlate primarily with species body mass, but more likely to species lifespan.{{clarify|"may ... primarily" versus "more likely" is confusing|date=August 2023}} Thus, the limited capacity of cells to replicate in culture may be directly relevant to the overall physical aging of an organism.<ref name="pmid13905659" /><ref name="pmid14315085" />

== See also ==
* [[Ageing]]
* [[Apoptosis]]
* [[Biological immortality]]
* [[HeLa|HeLa cells]]

== References ==
{{reflist}}

== Further reading ==
* {{Cite journal |last=Watts |first=Geoff |year=2011 |title=Leonard Hayflick and the limits of ageing |journal=The Lancet |volume=377 |issue=9783 |page=2075 |doi=10.1016/S0140-6736(11)60908-2 |pmid=21684371 |s2cid=205963134}}
* {{Cite journal |last=Harley |first=Calvin B. |last2=Futcher |first2=A. Bruce |last3=Greider |first3=Carol W. |year=1990 |title=Telomeres shorten during ageing of human fibroblasts |journal=Nature |volume=345 |issue=6274 |pages=458–60 |bibcode=1990Natur.345..458H |doi=10.1038/345458a0 |pmid=2342578 |s2cid=1145492}}
* {{Cite book |last=Gavrilov LA, Gavrilova NS |author-link=Leonid A. Gavrilov |title=The Biology of Life Span: A Quantitative Approach |publisher=Harwood Academic Publisher |year=1991 |isbn=3-7186-4983-7 |location=[[New York City|New York]]}}
* {{Cite journal |last=Gavrilov LA, Gavrilova NS |year=1993 |title=How many cell divisions in 'old' cells? |journal=Int. J. Geriatr. Psychiatry |volume=8 |issue=6 |page=528}}
* {{Cite journal |last=Wang |first=Richard C. |last2=Smogorzewska |first2=Agata |author-link2=Agata Smogorzewska |last3=De Lange |first3=Titia |author-link3=Titia de Lange |year=2004 |title=Homologous Recombination Generates T-Loop-Sized Deletions at Human Telomeres |journal=Cell |volume=119 |issue=3 |pages=355–68 |doi=10.1016/j.cell.2004.10.011 |pmid=15507207 |s2cid=10686288 |doi-access=free}}
* {{Cite journal |last=Watson |first=J. M. |last2=Shippen |first2=D. E. |year=2006 |title=Telomere Rapid Deletion Regulates Telomere Length in Arabidopsis thaliana |journal=Molecular and Cellular Biology |volume=27 |issue=5 |pages=1706–15 |doi=10.1128/MCB.02059-06 |pmc=1820464 |pmid=17189431}}

{{senescence}}
{{Authority control}}

{{DEFAULTSORT:Hayflick Limit}}
[[Category:Genetics]]
[[Category:Life extension]]
[[Category:Senescence]]
[[Category:Cellular senescence]]

Hayflick limit - История изменений

Admin: 1 версия импортирована

ru>Rich Smith: v2.05 - Fix errors for CW project (Reference list duplication - ISSN with incorrect syntax - ISSN with wrong checksum)