Telomere

The enzyme telomerase, through its influence on telomere length, is associated with health and mortality. Four pioneering randomized control trials, including a total of 190 participants, provided information on the effect of mindfulness meditation on telomerase. A meta-analytic effect size of d=0.46 indicated that mindfulness meditation leads to increased telomerase activity in peripheral blood mononuclear cells. These results suggest the need for further large-scale trials investigating optimal implementation of mindfulness meditation to facilitate telomerase functioning.

Understanding the malleable determinants of cellular aging is critical to understanding human longevity. Telomeres may provide a pathway for exploring this question. Telomeres are the protective caps at the ends of chromosomes. The length of telomeres offers insight into mitotic cell and possibly organismal longevity. Telomere length has now been linked to chronic stress exposure and depression. This raises the question of mechanism: How might cellular aging be modulated by psychological functioning?

The ethanol extract from the fruit of Terminalia chebula (Combretaceae) exhibited significant inhibitory activity on oxidative stress and the age-dependent shortening of the telomeric DNA length. In the peroxidation model using t-BuOOH, the T. chebula extract showed a notable cytoprotective effect on the HEK-N/F cells with 60.5 +/- 3.8% at a concentration of 50 microg/ml. In addition, the T. chebula extract exhibited a significant cytoprotective effect against UVB-induced oxidative damage.

For several decades simian virus 40 (SV40) early region genes have been used as a means of generating immortalized human cell lines; however, the molecular mechanisms of this process have begun to be understood only recently. SV40-induced immortalization proceeds via two phases. In the first phase ("lifespan extension"), cells continue proliferating for a limited number of population doublings beyond the point at which normal cells undergo senescence.

Normal human breast epithelial cells were transfected with expression vectors containing the p53 gene mutated at either codon 143, 175, 248 or 273, or by infection with a recombinant retroviral vector containing the p53 gene mutated at codons 143, 175, 248, or 273. The breast epithelial cells were monitored for extension of in vitro lifespan and immortalization. Expression of some, but not all, p53 mutants resulted in an extension of in vitro lifespan.

This study addresses the question of whether loss of p16INK4 expression contributes to the immortalization of human cells. In vitro immortalization usually proceeds through two phases. In the first phase (lifespan extension), cells continue proliferating and their telomeres continue shortening beyond the point at which normal cells become senescent. In the second phase (immortalization), the cells activate a telomere maintenance mechanism and acquire an unlimited proliferative potential.

This article reviews the current understanding of the involvement of telomerase in in vitro immortalisation of human cells. In vitro immortalisation with DNA tumour viruses or chemicals usually occurs in two phases. The first stage is an extension of lifespan beyond that at which cells would normally senescence, after which the culture enters a period of crisis. The second stage involves the escape from crisis of a rare cell in the culture, which goes on to proliferate indefinitely.

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.

Cell cycle checkpoints and tumor suppressor gene functions appear to be required for the maintenance of a stable genome in proliferating cells. In this study chromosomal destabilization was monitored in relation to telomere structure, lifespan control and G2 checkpoint function. Replicative senescence was inactivated in secondary cultures of human skin fibroblasts by expressing the human papillomavirus type 16 (HPV-16) E6 oncoprotein to inactivate p53. Chromosome aberrations were enumerated during in vitro aging of isogenic control (F5neo) and HPV-16E6-expressing (F5E6) fibroblasts.

The biology of telomeres and telomerase has been the subject of intensive investigative effort since it became evident that they play a significant role in two important biological processes, the loss of cellular replicative capacity inherent to organismal ageing and the unrestricted cell proliferation characteristic of carcinogenesis. Telomere shortening in normal cells is a result of DNA replication events, and reduction beyond a critical length is a signal for cellular senescence.