PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Senescent fibroblasts”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Effect of aluminum and lead salts on lipid peroxidation and cell survival in human skin fibroblasts.

The aim of this study was to see whether aluminum (Al) and lead (Pb) salts are toxic for cultured human fibroblasts under different experimental conditions, in the controllable situation offered by cell cultures. Cell survival and membrane lipid peroxidation served as markers of Al and Pb toxicity. Evaluation of the living cells was carried out using a colorimetric method, the mitochondrial reduction of 1-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). Lipoperoxidation assay was performed on whole cell homogenates by measuring thiobarbituric acid-reactive substances (TBARS) produced after incubation with ascorbic acid-ferrous sulfate. Al(III) and Pb(II) salts (300 microM) produce a considerable decrease in cell survival after an exposure period of 4d, evident with the three fetal calf serum concentrations in the culture media: 2, 5, and 10%. Taking into account in vitro cell aging, the cytotoxic effects of Al(III) and Pb(II) are greater in senescent fibroblasts than in young cells. Lead-induced cytotoxicity is higher than Al-induced cytotoxicity. A mechanism that contributes to cellular toxicity is membrane lipid peroxidation; our results demonstrate that Al(III) and Pb(II) ions, 400 microM, exert an antioxidant-like effect or a pro-oxidant action on cell membranes depending on exposure time. We describe significant increases in TBARS formation associated with the presence of 400 microM Al(III) or Pb(II) salts in the culture media. Our study also revealed that these heavy metals induce a cell age-dependent action on membrane lipoperoxidation that is greater in senescent fibroblasts and this could have severe consequences for maintenance of cellular integrity.

Aluminum Compounds↗
PubMed1983

Correlation between the presence of T-antigen and the reinitiation of host DNA synthesis in senescent human diploid fibroblasts after SV40 infection.

Senescent human diploid fibroblasts, TIG-1, had labelling indices of about 0.5-3% when labelled with [3H]thymidine for 3 days in fresh medium containing 10% fetal bovine serum. When these cells were infected with SV40, the percentage of nuclei incorporating [3H]thymidine increased by about 10-fold. The frequency of T-antigen-positive cells and that of [3H]thymidine-incorporating cells were almost the same. About 80% of T-antigen-positive cells were also positive to incorporation of [3H]thymidine, and the same result was obtained in infected young cells. These results indicated that senescent human diploid cells which are brought to synthesize T-antigen always initiate DNA synthesis as young cells do. The characteristics of senescent cells as compared with younger cells was low incidence of T-antigen-positive cells after infection. The basis of low susceptibility of senescent cells to initiate DNA synthesis by SV40 infection thus seems to be concerned with an event after the adsorption of virus, but before the synthesis of a detectable amount of T-antigen.

Antigens, Viral↗
PubMed1994

Id-related genes encoding helix-loop-helix proteins are required for G1 progression and are repressed in senescent human fibroblasts.

Three complete cDNA clones encoding Id-related helix-loop-helix (HLH) proteins lacking a basic region were isolated from a pcD2 cDNA expression library prepared from TIG-3 human diploid fibroblasts (HDF). Of these cDNAs (Id-1H, Id-1H', and Id-2H), two (Id-1H and Id-1H') appeared to be derived by alternative RNA splicing. Id-1H and Id-2H seem to be human homologues of mouse Id-1 and Id-2, respectively, and have potential to encode 154 and 135 amino acid proteins. The Id-1H and Id-2H mRNAs were barely detectable in quiescent early passage HDF; serum coordinately induced both mRNAs, with two peaks of expression, in early and late in G1. Antisense oligomers complementary to Id-1H and Id-2H mRNA prevented early passage HDF from entering the S phase of the cell cycle. The treatment of serum-stimulated early passage cells with the antisense Id-1H oligomer completely abolished Id-1H. In senescent cells, serum barely induced the Id-1H and Id-2H mRNAs, although the levels of c-myc expression induced were similar in early passage and senescent cells. The expression levels of these Id genes vary among immortal human cell lines. Both genes were overexpressed in VA4 SV40-transformed lung fibroblasts and EJ-1 bladder carcinoma cells, while these genes were expressed at a very low level in SVts8 cells derived from SV40 tsA-transformed TIG-3 cells. SVts8 cells may acquire some function redundant to Id proteins. HT1080 fibrosarcoma cells expressed the Id-1H gene but not the Id-2H gene, suggesting these Id genes may subserve redundant functions.

Alternative Splicing↗
PubMed1992

Reduction in heat shock gene expression correlates with increased thermosensitivity in senescent human fibroblasts.

The expression of three major classes of heat shock genes was examined in human diploid cells at differing in vitro ages. Metabolic labeling of cellular proteins following a brief heat shock showed that the synthesis of heat shock proteins was significantly reduced in late-passage cells. Northern blot analyses revealed that the reduced expression of heat shock proteins in old cells correlated with a reduced accumulation of heat shock-specific transcripts. The attenuation of heat shock gene activity in senescent cells was not unique to thermal stress since exposure of cells to sodium arsenite (10-50 microM) elicited a similar response. The reduced expression of heat shock gene products correlated with an increased thermal lability in late-passage cells following acute hyperthermic (49 degrees C) exposure. The preinduction of heat shock genes protected cells against the lethal effects of acute hyperthermia and abolished the increased thermal lability observed in senescent cells. The reduced expression of the heat shock response demonstrates that old cells possess a diminished ability to withstand adverse environmental conditions and maintain homeostasis.

Arsenic↗
PubMed2006

Shift in sphingolipid metabolism leads to an accumulation of ceramide in senescence.

Ceramide mediates the effects of several agonists leading to differentiation, apoptosis or senescence. We previously showed that ceramide becomes elevated in senescent fibroblasts. In the present study, senescent cultures of Wi-38 fibroblasts and human umbilical-vein endothelial cells were compared to low-passage cultures in order to identify which of the several pathways is predominantly responsible for the increased ceramide. We found that senescent cells take up the ceramide precursor [(3)H]palmitic acid and convert it to ceramide at essentially equivalent rates to their low-passage counterparts, suggesting that, as a whole, the inherent steps are unaltered. Analysis of subsequent steps, however, revealed changes in ceramide metabolism. The rate of ceramide conversion to sphingomyelin was reduced while glucosylceramide synthesis differed between the cell lines, while the rate of the reverse reactions tended to be increased in senescent cells. We also found a decrease in acidic but not alkaline ceramidase. The data show an overall change in favor increased ceramide levels. Of all of the pathways, neutral sphingomyelinase appears to be the most likely source of the senescence-associated ceramide. The relevance to mitosis and apoptosis are discussed.

Aging↗
PubMed2002

Telomerase rescues the expression levels of keratinocyte growth factor and insulin-like growth factor-II in senescent human fibroblasts.

Changes in expression levels of various cytokines, growth factors, and related genes were examined by reverse transcriptase polymerase chain reaction in a normal human fibroblast cell strain, TIG-3, along with in vitro aging. The expression levels of KGF and IGF-II were decreased with proliferative aging but not by growth arrest of young cells. In telomere-elongated cells prepared by transfection with human telomerase reverse transcriptase cDNA, high expression levels of these two genes were maintained, suggesting a causal relation between telomere shortening and reduced expression of KGF and IGF-II. The expression level of HGF was high in both growing and growth-arrested young cells but low in both senescent and telomere-elongated cells. The expression levels of follistatin and HB-EGF were high in both young growing and telomere-elongated cells but low in both senescent and growth-arrested young cells, indicating a growth-dependent expression. Expression levels of FGF-1, FGF-2, VEGF, BMP-3, and amphiregulin did not change with proliferative aging, growth arrest of young cells, or telomere elongation and life-span extension.

Aging↗
PubMed1990

Altered cell cycle responses to insulin-like growth factor I, but not platelet-derived growth factor and epidermal growth factor, in senescing human fibroblasts.

Human diploid fibroblasts (HDF) were used to study aging-related changes in the proliferative response to platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and insulin-like growth factor I (IGF-I, somatomedin-C) in serum-free, chemically defined culture medium. Cell cycle kinetic parameters were determined by using 5-bromodeoxyuridine incorporation and flow cytometric analysis with the DNA stain Hoechst 33258. This allowed analysis of the growth factor response to be focussed exclusively upon of the cycling faction of cells within the culture, even in senescent cell cultures which contained predominantly nondividing cells. PDGF and EGF exert their primary effect upon regulation of the proportion of cycling cells in the culture. The doses of PDGF and EGF that produced a half-maximal cycling fraction, analogous to Km, showed no large or consistent difference between young- and old-passage cells. In contrast, IGF-I primarily affects the rate of transition of cells from G1 into S phase, and the dose of IGF-I which produced a half-maximal rate of G1 exit increased up to 130-fold in older-passage cells. Unexpectedly, supraphysiologic concentrations of IGF-I were found to increase the G1 exit rate of the dividing subpopulation of cells in older-passage cultures to rates higher than those seen in young cultures. In summary, among cells capable of cycling in aging cultures, there were few changes in the regulation of the growth fraction by PDGF and EGF, but there was a greatly increased dependence on IGF-I for regulation of the rate of entry into S phase. The slower growth of the dividing population of cells in aging cultures may be related to a requirement for IGF-I at levels which are greatly above those usually supplied.

Cell Cycle↗
PubMed2001

Senescence and cytoskeleton: overproduction of vimentin induces senescent-like morphology in human fibroblasts.

One characteristic feature of senescent fibroblasts is flat, enlarged, and heterogeneous cell shapes. The present study was aimed to understand the structural basis of the senescent cell morphology. SDS-gel electrophoresis as well as western blotting demonstrated that there occurred a prominent protein band about 57 kDa in the senescent cells as compared with normal young or immortalized cells growing rapidly, and the protein was identified with a cytoskeletal protein, vimentin. In fact, senescent fibroblasts contained approximately threefold more vimentin protein, and fourfold more vimentin mRNA than young embryonic fibroblasts. In the senescent cells, vimentin cytoskeleton occurred as densely bundled filaments in parallel with the long axis of cell bodies, whereas in young or actively growing cells it showed short and thin vimentin filaments or fur-like irregular networks. It was further demonstrated that senescent cell shapes could be induced when a vimentin expression construct was transfected in young fibroblasts. These results suggest that senescent fibroblasts overproduce vimentin protein, and the overproduced vimentin filaments bring about the senescent cell morphology.

Adult↗
PubMed1977

Relationship of heat labile glucose-6-phosphate dehydrogenase and multiple molecular forms of the enzyme in senescent human fibroblasts.

Human fibroblasts derived from newborn foreskin and designated CF-3 were assayed for heat labile glucose-6-phosphate dehydrogenase (G6PD) when they had grown to confluency, as well as when they were arrested in an essentially nonmitotic state. Under both culture conditions there was an increase in heat labile G6PD (up to 25% of the total activity) as cells progressed through their in vitro lifespan; however, arrested cells exhibited less heat labile G6PD than did comparable growth controls (5-10% decrease). Acrylamide gel electrophoresis of crude G6PD preparations revealed three distinct bands of enzymatic activity. One of the bands was tentatively identified as the dimeric form of the enzyme and another as the tetrameric form. The tetrameric form was more heat sensitive, and the percent of the total activity of this form increased as the cells became senescent. The percent of total activity of the tetrameric form was comparable to the percent heat labile enzyme assayed at a given population doubling level. These results indicated that the observed increase in heat lability of G6PD with age may be due to a shift in equilibrium to the tetrameric form of the enzyme rather than the synthesis of aberrant enzyme molecules.

Cell Division↗
PubMed1987

Enhanced synthesis of a Mr = 55,000 dalton peptide by senescent human fibroblasts.

The secretory protein profiles of early and late passage cultures of human fibroblasts were compared using polyacrylamide gel electrophoresis. In comparison with early passage cell cultures (40-50% lifespan completed), late passage (greater than 80% of lifespan completed) cell cultures exhibited enhanced production of several peptides in the Mr range 55-60,000. One of those peptides had an apparent molecular weight of Mr = 55,000 and was constitutively present in the late passage cell conditioned medium. Late passage cell cultures synthesized the Mr = 55,000 peptide in the presence or absence of fetal bovine serum. Serum did not enhance its production by early passage cells. Further, production of the peptide was not induced in early passage cell cultures whose proliferation was arrested either by serum starvation or by contact inhibition. Pulse chase studies demonstrated that the peptide appears in the culture medium within 60 min of labeling. There was no evidence that it is derived via degradation of other proteins present either in early passage or late passage cell conditioned media. Further, the production of the 55,000 dalton peptide did not appear to be regulated by factors present in conditioned media. The peptide was detected in the conditioned media produced by late passage cultures of several different cell strains.

Cell Survival↗
PubMed1979

On the duration of mitotic stages in senescing human fibroblasts in culture.

The duration of three mitotic periods was measured by time-lapse cinemicrography in a line of normal human fibroblasts which displays the phenomenon of limited growth potential in vitro. It was found that the durations of metaphase and anaphase did not change as a function of passage level but that there was a statistically significant increase in the duration of cytokinesis. It was also found that there was no progressive increase in the variance of these periods between early and late passage cells. The data suggest that for those late passage cells which still retain the capacity to divide, the cellular mechanisms responsible for the synthesis of functional proteins, energy regulation and at least some membrane functions appear to be working normally.

Anaphase↗
PubMed1989

Note on the dispersion of generations among cells in senescing diploid fibroblast populations.

The cells in a cultured diploid fibroblast population have heterogeneous intermitotic times--even cells derived from the same mitosis may divide at different ages. This heterogeneity of inter-mitotic times results in asynchronous population growth and a dispersion of generations among members of the cell population. Because the appearance of non-dividing cells in middle-age populations has been attributed to the presence of lineages with more generations than average, we estimated the magnitude of the dispersion of cell generations as functions of the population doubling level and of the coefficient of variation of inter-mitotic times. For some data, such as that of Macieira-Coelho and Azzarone (Exp. Cell Res., 141 (1982) 325, the rate at which such non-proliferating lineages appear could be explained by a reasonable coefficient of variation of inter-mitotic times (25%). Most other data, however, would be fit only if the coefficient of variation of inter-mitotic times were 50% or greater, a variability that exceeds what has been observed in microcinematography experiments.

Cell Cycle↗