Characterization of a new human diploid cell line--IMR-91

The concept of telomeric non-reciprocal recombination (TENOR) applied to human fibroblasts grown in serial cultures: concordance with genealogical data

Since the discovery of the limited life span of human fibroblasts some 50 years ago, many genealogical studies have been undertaken to describe growth kinetics of fibroblasts in serial cultures by their individual division behavior. It is now accepted that proliferation capacities of human fibroblasts strongly depend on their telomere lengths and integrity. Telomeres shorten with each replication round, and there is a direct correlation between cell division capacity and telomere lengths; that is, the consumption of disposable telomeric DNA repeats during cell divisions progresses until critically short telomeres determining the replicative senescence of the cells are present. Recently, we have suggested that telomeres in fibroblasts can also become elongated during DNA replication by telomeric non-reciprocal recombination (TENOR). Here we discuss genealogical data collected over the last decades as well as more recent findings on the telomere-driven replicative senescence process, and we summarize both to give an integrated picture.

Changes in the cell surface of human diploid fibroblasts during cellular aging

The electrophoretic mobility of 13 human diploid cell strains, TIG-1, TIG-2, TIG-3, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, TIG-1H, TIG-1L, TIG-2M, TIG-2B, and TIG-3S, which were established from different tissues of human embryos, was studied at different passages. The net negative surface charge of the cells was characteristic for each cell strain and decreased significantly during the in vitro aging of the cells. The decrease in the net negative charge of the cells correlated well with the decrease in cell density throughout the life span of the cells. A strict linear correlation between the electrophoretic mobility and the number of cells harvested at each passage was obtained for all the human diploid cell strains. Moreover, almost the same linear regression coefficient of the cells was obtained among these cell strains. Therefore, the net negative surface charge of human diploid cell strains could serve as a cell surface marker for in vitro cellular aging.

Decline of poly(ADP-ribosyl)ation during in vitro senescence in human diploid fibroblasts

Poly(ADP-ribose) polymerase activity was determined at various times during the in vitro life span of two human diploid fibroblast-like cell lines of different donor ages. The cell lines differed in their ability to transfer ADP-ribose, with cells from an embryonic donor exhibiting 2 to 3 times the activity found in cells obtained from a newborn donor. The activity in both cell lines decreased by 30-60% as the cells moved through their in vitro life spans. The decline could not be attributed to increases in glycohydrolase or the leakage of polymerase from older cell preparations. Enzyme activation with DNase I indicated that similar levels of enzyme were present in both cell lines at all in vitro ages. These results indicate that although poly(ADP-ribosyl)ation is inversely related to donor age as well as in vitro age the decrease is in response to other factors which change with increasing age.

Isozyme polymorphisms in human diploid cell strains for research on cellular aging

Six human lung diploid cell strains established for the study of in vitro cellular aging (TIG-1, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, and HeLa cells as a control) were studied by cellulose acetate membrane electrophoresis for allozymic differences at 18 enzyme loci. Eight enzyme loci (G6PD, PGM1, PGM3, PepA, PGD, ADA, GLO1, and ME), proved to be informative in establishing unique allozyme genetic signatures for all of the cell strains established from the same species and from the same organ. Changes in the allozyme genetic signatures were not observed throughout the life span of TIG-1 and MRC-9 cells. The allozyme genetic signatures can be used as a quick monitor of cell identification and intraspecific cell contamination.

A new human male diploid cell strain, TIG-7: its age-related changes and comparison with a matched female TIG-1 cell strain

A new human diploid cell strain, TIG-7, which has the male karyotype, was established and characterized. Isozyme and histocompatibility typing of the cell strain was performed. The average in vitro life span of the cells is 73 population doublings. Changes in cell volume, doubling time, saturation density, the efficiency of cell attachment, plating efficiency, and relative DNA content were examined during in vitro cellular aging. Hydrocortisone slightly prolongs the life span of the cell strain when the hormone is administered to the cultures during middle passages. The age-related changes in the parameters of TIG-7 are not appreciably different from those of the previously established TIG-1 cell strain. These results show that this cell strain is useful for research on cellular aging; further profit is anticipated from research using a combination of these two sexually different cell strains.

Fixation and repair of radiation-induced potentially mutagenic damage sensitive to hypertonic treatment in human diploid fibroblasts

The effect of hypertonic salt treatment on the repair of potentially lethal damage and potentially mutagenic damage in X-irradiated asynchronous and synchronous human diploid fibroblasts (IMR91) have been studied. Resistance to 6-thioguanine was used for the mutagenic end point. When cells in late-S-phase were treated with hypertonic salt solution immediately after X-irradiation, both cell killing and mutation induction were enhanced, as compared to X-irradiation alone. This suggests that X-irradiation of cells in late S phase induces both potentially lethal damage and potentially mutagenic damage and that both are sensitive to hypertonic salt solution. When cells were allowed 2 h for repair after exposure to X-rays, both types of damage were completely repaired. Almost the same results were obtained with asynchronous cells. These results are discussed in terms of the relationship between radiation damage leading to cell lethality and mutagenesis.

Histone gene stability during cellular senescence

The extent to which human histone gene organization is conserved during the in vitro lifespan of human diploid fibroblast-like cells was determined by comparing the restriction patterns of a human H4 and an H3 histone gene from cells of various in vitro ages. No age related change in the organization of these two genes was detected.

Human histone gene organization. Identification of a histone gene polymorphism prevalent in a black population

Analysis of the restriction enzyme digests of total genomic DNAs from a broad spectrum of human cell lines and from individuals with different genetic backgrounds, by hybridization with a series of cloned human histone sequences, indicated restriction site polymorphisms (RSPs) for two adjacent human histone genes which reside on chromosome 1. In most cell lines and individuals examined we observed a single 2.05 kb H4 histone HindIII fragment and a 7.0 kb H3 histone HindIII fragment. In contrast, the polymorphisms were manifested as a 2.15 kb H4 HindIII fragment and a 9.1 kb H3 HindIII fragment. From population studies, we were able to show that there is no linkage disequilibrium between these two polymorphic restriction sites. Nor was there any apparent correlation between the presence of the H3/H4 histone polymorphisms and maintenance of the transformed karyotype, passage in culture, transformation or tumor progression. These chromosome 1 H3 and H4 histone gene polymorphisms are common in the American Black population and, in our survey of individuals, were not found in the American Caucasian population. Among the American Blacks studied, the frequency of the H3 HindIII(-) allele is 43% and of the H4 HindIII(-) allele 30%. In limited family studies, we were unable to detect recombination between these two physically linked alleles.