Proceedings of the National Academy of Sciences of the United States of America
Inclusion of vitamin E (DL-alpha-tocopherol) in the culture medium for human diploid cells greatly prolongs their in vitro lifespan. The addition of 100 mug of DL-alpha-tocopherol per ml of medium has allowed us to culture WI-38 cells for more than 100 population doublings to date. (These cells normally have an in vitro lifespan of 50 +/- 10 population doublings.) Cells at the 100th population doubling have a normal diploid karyotype, appear to behave in all other respects like young WI-38 cells, and are still actively dividing.
It has been shown that human diploid cells from various donor ages can be arrested in an essentially nonmitotic state by reducing the serum concentration of the incubation medium from 10 to 0.5 percent. Cells incubated at this serum level maintained the population distribution that was present when the cells reached confluency. The population, which has 90 percent of the cells in the G1 phase of the division cycle, was not static and exhibited a low level of mitotic activity with prolonged interdivision times.
Normal human diploid cells, TIG-1, ceased to proliferate at about the 62 population doubling level (PDL). Transformed clones isolated from TIG-1 cells infected with wtSV40 and those with tsA900 SV40 cultured at 34 degrees C were subcultured up to about 80 PDL. When the culture temperature of tsA SV40-transformed cells was shifted from 34 to 39.5 degrees C at 51 PDL, the growth curve of these transformed cells changed to that of normal young cells.
International Journal of Cancer. Journal International Du Cancer
Dermal fibroblasts from patients with the autosomal dominant cancer-prone disease Basal Cell Nevus Syndrome (BCNS) exhibit a serum dependence, anchorage dependence and in vitro lifespan (about 20 population doublings or less) similar to those of fibroblasts from normal age-, race- and sex-matched controls.
Infection of normal human diploid fibroblasts (HF) with the DNA tumor virus simian virus 40 (SV) leads to an extension of lifespan and concomitant increase in the levels of the viral large tumor antigen (T antigen) and the cellular protein p53. The intracellular localization of T antigen and p53 was mostly nuclear in both SVpre-crisis and SVpost-crisis cells, however certain population doubling (PD) of the SVpre-crisis cells exhibited some cytoplasmic staining. The DNA content of SVpre-crisis cells shifted to tetraploidy and the SVpost-crisis cells were near-tetraploid.
Telomere loss has been proposed as a mechanism for counting cell divisions during aging in normal somatic cells. How such a mitotic clock initiates the intracellular signalling events that culminate in G1 cell cycle arrest and senescence to restrict the lifespan of normal human cells is not known. We investigated the possibility that critically short telomere length activates a DNA damage response pathway involving p53 and p21(WAF1) in aging cells.
Telomere shortening in normal human cells causes replicative senescence, a p53-dependent growth arrest state, which is thought to represent an innate defence against tumour progression. However, although it has been postulated that critical telomere loss generates a 'DNA damage' signal, the signalling pathway(s) that alerts cells to short dysfunctional telomeres remains only partially defined.
Biochemical and Biophysical Research Communications
Telomere is the repetitive DNA sequence at the end of chromosomes, which shortens progressively with cell division and limits the replicative potential of normal human somatic cells. L-carnosine, a naturally occurring dipeptide, has been reported to delay the replicative senescence, and extend the lifespan of cultured human diploid fibroblasts. In this work, we studied the effect of carnosine on the telomeric DNA of cultured human fetal lung fibroblast cells.
Dietary restriction (DR) increases lifespan in a range of evolutionarily distinct species. The polyphenol resveratrol may be a dietary mimetic of some effects of DR. The pivotal role of the mammalian histone deacetylase (HDAC) Sirt1, and its homologue in other organisms, in mediating the effects of both DR and resveratrol on lifespan/ageing suggests it may be the common conduit through which these dietary interventions influence ageing.
The lengths of human telomeres, which protect chromosome ends from degradation and end fusions, are crucial determinants of cell lifespan. During embryogenesis and in cancer, the telomerase enzyme counteracts telomeric DNA shortening. As shown in cancer cells, human telomerase binds the shelterin component TPP1 at telomeres during the S phase of the cell cycle, and adds ~60 nucleotides in a single round of extension, after which telomerase is turned off by unknown mechanisms.