Replicative aging

The ability of cells to divide is limited. As the passages progress, morphological, biochemical and molecular changes related to the aging process are evident in vitro cell cultures. After a certain number of cycles, cells such as human fibroblasts (the most commonly used cell model of "normal" cells) stop dividing, even if the culture medium provides all the necessary nutrients. The limitation of the number of cell cycles is the essence of the so-called replicative aging (senescence), which eventually leads to the arrest of the cell cycle in the G1 phase of interphase. However, cells do not have to die after replication has stopped, they can remain in this stage for several years in cell culture with regular replacement of the culture medium.

The division frequency of human fibroblasts cultured in vitro and the subsequent arrest of mitotic activity were described in 1961 by L. Hayflick and P. Moorhead. Later, similar results were obtained on other types of cell cultures: epidermal keratinocytes, endothelial, adrenocortical, glial cells, T-lymphocytes, &beta;-buňkách pankreatu β-cells or smooth muscle cells. The limitation of cell proliferation in vitro is called the Hayflick limit. On average, human cells can go through about 50 cell cycles in vitro. Unlike cell lines derived from normal cells, tumor cells can be cultivated indefinitely. A classic example is the cervical carcinoma cell line (HeLa), which has been maintained for more than 50 years. Closely related to replicative aging is the length of telomeres, the indispensable terminal parts of the nuclear chromosomes of eukaryotes.

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