Increased nuclear sizes in senescent human diploid fibroblast cultures

Culture media variation as related to in vitro aging of human fibroblasts: I. Effects on population doubling, nuclear volume and nuclear morphology

The relative effect of five commonly used culture media (MEM, BME, McCoy's 5A, M199 and HMEM) on the population doubling level (PDL), nuclear volume and nuclear morphology was examined during in vitro senescence of WI-38 human fetal fibroblasts. Statistical analyses showed that cells grown in M199 had a significantly lower PDL than that of cells cultured in any other medium. The PDL in McCoy's 5A was significantly lower compared to that in BME, MEM and HMEM. Cells grown in BME, MEM and HMEM showed similar PDL. It was found that the nuclei of aged cells grown in M199 were significantly larger in volume than cells aged in any other medium. The average increases in nuclear volume of cells during aging in BME, MEM and McCoy's 5A were statistically equivalent. The increase in nuclear volume in HMEM was significantly smaller than that of cells aging in M199 and was longer than that of cells aging in BME or MEM. Linear regression analysis showed that there was a linear increase in nuclear volume as a function of PDL for cells aged in all five media. However, the rate of increase in nuclear volume with increasing PDL varied from medium to medium. There was no significant difference between media on induction of abnormal nuclear morphology as related to PDL. The relative effects of all five media were not uniform on the three cellular parameters investigated during in vitro aging of WI-38 cells. It is, therefore, suggested that one should keep this medium differential in mind to allow meaningful comparison of possible changes in various morphological parameters during in vitro senescence of diploid human fibroblasts such as WI-38.

Donor-age-related changes in the morphology, growth potential, and collagen biosynthesis in rat fibroblast subpopulations in vitro

Primary explant, mass and clonal fibroblast cultures established from BN rat skin and lungs were used to examine changes in cell behaviour associated with aging. Three distinct fibroblast cell types, i.e. FI, FII and FIII, could be identified on the basis of their morphological and proliferative properties. They could also be distinguished from each other by the amount and type of collagen they synthesized in clonal cultures. FI cells are diploid, spindle shaped and highly proliferative, and they synthesize low levels of type-I and -III collagen. Epithelioid FII cells are also diploid, proliferate slowly, and exhibited elevated collagen synthesis as compared to FI cells. FIII fibroblasts are large, stellate, tetraploid cells that proliferate more slowly than the other types but synthesize large amounts of collagen. In comparison to FI cells, the level of type-III-collagen synthesis is slightly elevated in FIII fibroblasts. In primary explant, mass and clonal cultures, the relative proportions of FI, FII and FIII cells were found to change as a function of the age of the donor animal. The increasing predominance of FIII cells in mass cultures of fibroblasts obtained from donors of increasing ages was consistent with the increased level of collagen synthesis in these cultures. Our observations indicate that the differentiation of normal BN rat fibroblasts occurs via a three-phase process. We discuss the age-related changes in the relative abundance of FI, FII and FIII cells in vivo in the context of alterations in fibroblast replacement and changes in connective tissue that occur during aging.

Induction of DNA polymerase alpha in senescent cultures of normal and Werner's syndrome cultured skin fibroblasts

DNA polymerase alpha activity was determined following serum stimulation of early and late passages of human diploid fibroblast-like (HDFL) cultures derived from apparently normal donors (two strains) and from a patient with Werner's syndrome (one strain). Induction of this enzyme was observed in both low passage, actively proliferating cultures and in postmitotic "senescent" cultures from all three strains. The maximal polymerase activity of early and late passage cells of each strain were nearly identical when normalized to the number of cells present. However, the activity of the enzyme was observed to be significantly lower in late passage cultures when normalized to total protein content apparently because of enlargement of the senescent cells. The behavior of Werner derived cells was similar to that of the normal cells. The induction of DNA polymerase alpha in senescent cultures indicates that they retain the capacity to carry out some complex metabolic responses to mitogen stimulation. In addition, these results suggest the possibility that dilution of DNA polymerase alpha and/or other DNA replication factors may play a role in the onset or maintenance of the postmitotic state in the enlarged senescent HDFL cells.

Does capacity of DNA replication change during in vitro ageing?

We described elsewhere how a lack of change in the rate of DNA chain elongation occurred during in vitro ageing of human diploid fibroblasts. Here we further examined the rate of actual incorporation of tritiated thymidine, the center-to-center distance of replicons and the length of each phase of the cell cycle in order to extend our previous results to the other aspects of DNA replication. The results obtained showed that the rate of net DNA synthesis, the replicon size and the duration of S phase did not change during in vitro ageing. Our findings indicated that the reason why the greater part of the cell population at high population doubling levels becomes incapable of proliferating might not be the gradual decline in the ability of DNA replication. The regulation system(s) of DNA replication may alter during the period of culturing without any change in the capacities of the DNA replication machinery and, consequently, the non-cycling cells increase.

Cell surface changes in senescent and Werner's syndrome fibroblasts: their role in cell proliferation

Cell surface is known to participate in the regulation of cell proliferation through interaction with adjacent cell surfaces or the extracellular matrix, or both. A clinical survey of the Werner syndrome suggests some disorders in glycosaminoglycan metabolism. Also, the skin fibroblasts derived from the patients with WS have a reduced proliferation capacity. We here examined, in vitro and in vivo, alterations of the cell-surface properties of WS cells and aging human fibroblasts. Cell-surface negative charges, examined by electrophoretic mobility of dispersed single cells in buffer, were seen to decline steadily as a function of cumulative population doublings. A strict linear relationship was found between electrophoretic mobility (micron/sec/V/cm) and number of cells harvested at each passage in all cell lines examined. The slope of this line in cells from donors of different ages indicated that WS fibroblasts resemble cells from much older normal controls. The same conclusion was drawn from our previous study of Con A-mediated red cell adsorption, which was confirmed as reflecting an alteration of cell-surface coat negative charge. Electrophoretic mobility after treatment of cell surface with degradative enzymes showed that the cell-surface negative charges were attributable to sialic acid, chondroitin sulphates, hyaluronic acid, and heparan sulphate. Two-dimensional electrophoresis of 3H-glucosamine incorporated glycosaminoglycans (GAGs) revealed that heparan sulphate was the main component of GAGs on the fibroblast cell surface and that the relative amount of heparan sulphate among GAGs on the cell surface increased in vitro with the number of passages. Growth kinetics of fibroblasts on sheets of fixed cells treated with a fixative (glutaraldehyde) and degradative enzymes were examined to elucidate the role of cell-surface GAGs in the regulation of cell proliferation. Cell growth was inhibited 40% when the fibroblasts were cultured on the fixed sheets of late passage cells. Treatment of the fixed cell sheets with heparitinase or nitrous acid resulted in complete recovery from the growth inhibition. Cell growth on sheets of fixed cells derived from young, middle, and senescent fibroblasts showed that the surface of the senescent cells had the greatest inhibitory effect. These inhibitory effects of fixed cell sheets correlated well with both the amount of heparan sulphate relative to the total GAGs on the surface and to the saturation density of cell growth at each passage. These findings strongly suggest that heparan sulphate, or its complex, on the cell surface is involved in the regulation of cell proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Correlation of DNA repair synthesis with ageing in mice, evidenced by quantitative autoradiography

Fibroblasts from C57B1/6 female mice of different age have been treated with short-wave ultraviolet light. The amount of unscheduled DNA synthesis in the fibroblasts, determined by quantitative histoautoradiography, decreases with the donor's age. This result is discussed with regard to an increase in nuclear area and modifications of cell population dynamics with age. Moreover, differences between individuals of the same age group with regards to unscheduled DNA synthesis have been observed.

Identification and characterization of non-dividing cell populations in phase II cultures of human glial cells

It has been reported that cultures of normal cells in phase II contain a non-multiplying cell population, the size of which increases with passage number. In phase II cultures of normal human glial cells we have found two subpopulations of non-proliferating cells, one of which has a characteristic morphology, and differs from the actively dividing cells in a number of respects: (1) they are larger although of various sizes and are well spread over a very large substratum area: (2) they contain a great number of granules showing acid phosphatase activity, being heavy metal positive and displaying the characteristic natural fluorescence of lipofuscin pigment; and (3) they frequently contained a central somewhat irregular nucleus with various numbers of darkly staining nucleolar-like structures. Cytophotometric nuclear DNA measurements of the described "large" cell population show a decreased proportion of diploid cells as compared to their smaller sister cells. Moreover, with increasing passage number, the DNA values for large cells shift towards higher ploidy levels resulting in a scattered aneuploid pattern in the oldest passage. This "large" cell subpopulation consists of between 2% and 3% of all passages and becomes greatly decreased following subcultivation. The other subpopulation of non-dividing cells is generally morphologically similar to the dividers, increases in size with passage number and is the more important in the phase III phenomenon.

Effects of beta interferon on human fibroblasts at different population doubling levels. Proliferation, cell volume, thymidine uptake, and DNA synthesis

Cellular aging had no effect on the ability of beta interferon to increase cell volume and population doubling time in 76-109 cells, a line of human skin fibroblasts. However, DNA synthesis in cells at high population doubling levels (PDL 55-70) was inhibited after 72 h of beta interferon treatment (1,000 U/ml) while no inhibition of DNA synthesis was observed in cells at middle population doubling levels (PDL 30-40).

Thymidine triphosphate synthesis in senescent WI38 cells. Relationship to loss of replicative capacity

The effect of in vitro age on thymidine triphosphate (TTP) synthesis was assessed in WI38 cultures according to the following measurements: (1) thymidine kinase activity of broken cell preparations; (2) in situ incorporation of [3H]thymidine into acid-soluble material; and (3) total intracellular TTP content as determined by an enzymatic assay. All three parameters were maximal in exponentially proliferating populations and minimal in quiescent monolayers; no significant differences between young and old cultures were observed despite the reduced replicative capacity of the latter. The addition of serum to density-arrested cultures induced both TTP synthesis and DNA replication after a lag of approx. 12 h; although a greater percentage of young cells initiated replication as compared with old, pool sizes expanded to a similar extent in both populations. Pool expansion did not require entry into S phase; the pool sizes of control and cytosyl arabinoside-treated cultures were comparable. These findings suggest that senescent cells retain the ability to synthesize TTP, even though they are incapable of replicating DNA. Because TTP synthesis is a cell cycle-dependent event that normally begins in late G1, senescent cells might be blocked in the latter portion of the prereplicative phase and not in G0 as are quiescent cells.

Isolation by flow sorting of cytokinetic and morphological heterogeneity in late-passage cultures of human diploid fibroblasts (IMR-90)

Considerable structural, metabolic, and proliferative heterogeneity develops in populations of cultured diploid cells which have reached advanced levels of population doubling. Isolation of noncycling cells from late-passage cultures would permit more definitive investigation of the structure and behavior of individual senescent cells. In this paper, we report the viable sorting of late-passage cultures of human diploid fibroblasts (IMR-90) into two subpopulations of cells with different proliferative potentials. Sorting is based on cellular light-scattering properties and autofluorescence. Structural and behavioral features of the subpopulation exhibiting increased forward-angle light scatter are more characteristic of senescent cells than the subpopulation sorted by decreased forward-angle light scatter.

Gene dosage effects in human diploid and tetraploid fibroblasts

The effects of cell ploidy on the biochemical characteristics of cultured cells were compared using human diploid vs tetraploid fibroblasts isolated with a non-selective method. Their DNA replication was compared by thymidine incorporation, and DNA content by Feulgen staining and quantitative analysis. Their RNA and protein content, cell sizes and the specific activities of glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) were assayed quantitatively. With the exception of RNA content, all other parameters demonstrated a 2-fold increase reflecting the increase in cell ploidy. These direct gene dosage effects on the genetic material and functional expression of the human genome were in contrast to previous observations in other species and validate the use of human intraspecific euploid hybrids for biochemical and genetic studies.

Evidence that healthy human gingiva contains functionally heterogeneous fibroblast subpopulations

Six mass cultures of human fibroblasts derived from a single biopsy of a normal gingival papilla tip were studied with regard to their protein, collagen and glycosaminoglycan synthesis in vitro, using incorporation of radiolabelled substances. The proliferation rates, replicative life-spans and cell-size distributions of these mass cultures were determined. There were significant differences among the 6 cultures and these differences persisted throughout numerous cell replications in vitro. It is suggested that functional heterogeneity exists among phenotypically stable fibroblast subpopulations or subpopulation mixtures from normal tissue. The concept of participation of fibroblast subpopulations in disease pathogenesis is supported by these preliminary findings.

Comparison between proliferative changes and nuclear events during ageing of human fibroblasts in vitro

Age-related alterations in nucleoproteins were examined in resting human embryonic fibroblasts at various population doubling levels (PDL) with three techniques for electron microscopy. Conventional glutaraldehyde fixation showed nuclear modifications consistent with previously published studies. Miller's technique permitted the detection of transcription complexes in young as well as in old cells. The technique involving the ultrathin sectioning of partially loosened nucleoproteins revealed at high PDL a marked rarefaction of the chromatin threads and the appearance of large parts of the lamina densa devoid of attached threads. In addition, the nucleolar filamentous masses were considerably less tufty than at earlier PDL, suggesting a decrease in the ribosomal transcriptional activity. These changes in nucleoprotein organization were rare before the 40th PDL, then increased to about 5% of the nuclei when the percentage of cells initiating DNA during the first 24 h remained at low levels. They were the rule for the last 6 to 7 PDL and coincided with the time when the maximal densities started to fall rapidly. They appeared after treatment with a loosening medium at neutral and at alkaline pH.

Cell culture aging

Cellular research in aging has been stimulated by the observation that human diploid cells have a limited number of cell divisions in culture. This loss of cellular proliferation (in vitro senescence) has been extensively studied by biochemical, clonal, and genetic analysis. Studies of human skin fibroblast cultures have revealed that in vitro senescense is related to in vivo human cellular aging. Recently differentiated cells have been proposed for aging studies. These cells may provide additional information on aging since alterations of in vitro cellular functions may be related to the in vivo behavior of specific differented cell types.

Interferon effects on microfilament organization, cellular fibronectin distribution, and cell motility in human fibroblasts

We have shown previously (Pfeffer et al., 1979, Exp. Cell Res. 121:111-120) that treatment of human fibroblasts, planted at a density of 2x10(3) cells/cm(2), with purified human fibroblasts interferon (640 U/ml) for 3 d at 37 degrees C decreases the overall rate of cell proliferation to 35-40 percent of the control value. In the present experiments we have characterized the phenotype of interferon-inhibited fibroblasts. The mean volume of trypsinized, interferon-treated cells was increased 31 percent abover that of control cells. The interferon-treated population was much more heterogeneous than the control population with respect to volume, and there was a considerable overlap in the volume distributions of the two populations. The cell surface area was, on the average, increased 65 percent after interferon treatment. More than 80 percent of the treated cells had enlarged nuclei, many of which were lobed, and the fraction of binucleated cells was increased fivefold. After interferon treatment, over 40 percent of the cells showed large actin-containing fibers in the form of multiple parallel arrays. Fewer than 5 percent of the control cells contained such large actin fibers. The number of actin fibers of all sizes was tripled in the treated fibroblasts on a per cell basis and, calculated per unit surface area of the cells, the number was increased 82 percent. In contrast, 10-nm filaments and microtubules did not appear to be increased in number per unit surface area of the cells. The increases per cell in the abundance of these structures were directly related to increased cell size. After interferon treatment, fibronection was distributed in arrays of long filaments covering most portions of the cell surface. Interferon treatment markedly decreased the rate of cell locomotion as well as membrane ruffling and saltatory movements of intracellular granules.

Quantitation of DNA repair in brain cell cultures: implications for autoradiographic analysis of mixed cell populations

Quantitation of DNA repair in the mixed cell population of mouse embryo brain cultures has been assessed by autoradiographic analysis of unscheduled DNA synthesis following UV-irradiation. The proportion of labelled neurons and the grain density over neuronal nuclei are both less than the corresponding values for glial cells. The nuclear geometries of these two classes of cell are very different. Partial correction for the different geometries by relating grain density to nuclear area brings estimates of neuronal and glial DNA repair synthesis more closely in line. These findings have general implications for autoradiographic measurement of DNA repair in mixed cell populations and in differentiated versus dividing cells.

Cytological changes senescing WI-38 cells: a statistical analysis

Changes in the cell, nuclear, nucleolar dry masses and areas were monitored simultaneously during in vitro senescence of WI-38 human fetal lung fibroblast cells, and the results were analyzed statistically. There was a two-step increase in all six parameters studied, following an initial decrease. The patterns of increase were strikingly similar for all six measures, i.e., an initial lag period was followed by a sharp increase, a plateau and a final, abrupt increase. In all cases, there was a strong correlation between corresponding area and dry mass measurements for each cell component. The dry mass/area ratio also increased as a function of in vitro aging and ultimately doubled in value. Weak intrapassage correlations between cell, nuclear and nucleolar dry masses indicated that there were passage to passage differences in the relative rates of dry mass increases which were not apparent over long periods of growth. The increases in all muclear and nucleolar areas were interdependent until the last doubling where they increased independently. The standard deviation for all six parameters increased as a function of in vitro senescence indicating that there was an increase in the heterogeneity of cells relative to these parameters.

Nucleolar changes in senescing WI-38 cells

Changes in the area, dry mass and morphology of nucleoli were studied during in vitro aging of WI-38 cells. Interferometric methods were used for nucleolar dry mass determinations. The results show that there is (1) an increase in the fraction of cells with one large nucleolus per nucleus, 17% at population doubling 27.3 vs. 93% at population doubling 41.2, (2) an increase in mean nucleolar dry mass (583% at the last doubling), and (3) an increase in mean nucleolar area (236% at the last doubling) with in vitro senescence of WI-38 fibroblast cells. A strong correlation (r = 0.92) between nucleolar dry mass and nucleolar area was demonstrated.

Nuclear area changes in senescing human diploid fibroblasts

The pattern of mean nuclear area changes was determined in human fibroblast cell strains from male donors of three different ages (8,40 and 84 years) during their in vitro lifespan. There was a statistically significant increase in mean nuclear area of cells of all three strains during their aging in vitro. A gradual increase of the subpopulation of cells with larger nuclei was also observed. Evidence for a positive correlation between aging in vitro, as reflected by mean nuclear areas at the tenth doubling from the end of in vitro doubling activity, and donor age is presented.

The relationship between in vitro cellular aging and in vivo human age

Differences between early and late passage cell cultures on the organelle and macromolecular levels have been attributed to cellular "aging". However, concern has been expressed over whether changes in diploid cell populations after serial passage in vitro accurately reflect human cellular aging in vivo. Studies were therefore undertaken to determine if significant differences would be observed in the in vitro lifespans of skin fibroblast cultures from old and young normal, non-hospitalized volunteers and to examine if parameters that change with in vitro "aging" are altered as a function of age in vivo. Statistically signigificant (P less than 0.05) decreases were found in the rate of fibroblast migration, onset of cell culture senescence, in vitro lifespan, cell population replication rate, and cell number at confluency of fibroblast cultures derived from the old donor group when compared to parallel cultures from young donors. No significant differences were observed in modal cell volumes and cellular macromolecular contents. The differences observed in cell cultures from old and young donors were quantitatively and qualitatively distinct from those cellular alterations observed in early and late passage WI-38 cells (in vitro "aging"). Therefore, although early and late passage cultures of human diploid cells may provide an important cell system for examining loss of replicative potential, fibroblast cultures derived from old and young human donors may be a more appropriate model system for studying human cellular aging.

Relationship between cell replication and volume in senescent human diploid fibroblasts

Since alterations in cell replication rate and cell volume distribution are two of the earliest changes seen in the culture of human diploid cells, it was decided to examine the relationship between these parameters. After standardization of the conditions for cell volume measurements (enzyme treatment, temperature and stage of cell growth), a close correlation was observed between cell population doubling time and cell volume in WI-38 cells at various levels of in vitro passage. Cell populations which replicate more slowly (trisomic-21 fibroblasts, fetal skin fibroblasts) also demonstrated a shift to larger cell volumes when compared with control rapidly replicating cell populations at the same level of in vitro passage. Similar shifts to larger cell volumes were produced by reducing serum concentration, decreasing incubation temperature and inhibiting DNA synthesis. Separation of senescent WI-38 cells on the basis of cell volume revealed that the cell fractions with the largest modal cell volume contained the highest percentage of slow or nonreplicating cells. Therefore, an inverse relationship appears to exist between growth rate and cell volume in cultured human diploid fibroblasts.