Strict relationship between dialyzed serum concentration and cellular life span in vitro

Success Rate of Grafts With Multiple Renal Vessels in 3136 Kidney Transplants

OBJECTIVES

Multiple renal vessels are often detected in living and deceased organ donors. In the past, transplant with multiple renal vessel grafts has been a contraindication because of high vascular and urological complication rates. However, improvements in vascular reconstruction and anastomosis techniques have allowed graft function to be maintained for many years. Here, we retrospectively evaluated transplant of multiple renal vessel grafts and graft survival and postoperative vascular and urological complications.

MATERIALS AND METHODS

From November 1975 to July 2020, there were 3136 renal transplants (716 deceased donors, 2420 living donors) performed in our center. There were 2167 living donors and 643 deceased donors with single renal vessel grafts and 253 living donors and 73 deceased donors with multiple renal vessel grafts. For anastomoses, external iliac, internal iliac, common iliac, and inferior epigastric arteries and external iliac veins were used. Cold ischemia time, anastomosis time, postoperative vascular and urological complications, acute tubular necrosis, creatinine clearance, serum creatinine levels, graft rejection episodes, and graft and patient survival rates were evaluated.

RESULTS

With regard to creatinine clearance, cold ischemia and anastomosis time, acute tubular necrosis, rejection episodes, and 1-, 2-, and 5-year posttransplant serum creatinine levels, there were no significant differences between the groups. Graft survival rates in the single renal vessel group were 92.9% at 1 year posttransplant and 78.3% at 5 years posttransplant; rates in the multiple renal vessel group were 93.1% at 1 year and 79.7% at 5 years. The corresponding patient survival rates were 95.5% (1 year) and 92.9% (5 years) for the single renal vessel group and 96.9% (1 year) and 87.2% (5 years) for the multiple renal vessel group.

CONCLUSIONS

Improved anastomosis and recon struction techniques have allowed the safe transplant of multiple renal vessel grafts that may remain functional for many years.

Identification of differentially regulated secretome components during skeletal myogenesis

Myogenesis is a well-characterized program of cellular differentiation that is exquisitely sensitive to the extracellular milieu. Systematic characterization of the myogenic secretome (i.e. the ensemble of secreted proteins) is, therefore, warranted for the identification of novel secretome components that regulate both the pluripotency of these progenitor mesenchymal cells, and also their commitment and passage through the differentiation program. Previously, we have successfully identified 26 secreted proteins in the mouse skeletal muscle cell line C2C12 (1). In an effort to attain a more comprehensive picture of the regulation of myogenesis by its extracellular milieu, quantitative profiling employing stable isotope labeling by amino acids in cell culture was implemented in conjunction with two parallel high throughput online reverse phase liquid chromatography-tandem mass spectrometry systems. In summary, 34 secreted proteins were quantified, 30 of which were shown to be differentially expressed during muscle development. Intriguingly, our analysis has revealed several novel up- and down-regulated secretome components that may have critical biological relevance for both the maintenance of pluripotency and the passage of cells through the differentiation program. In particular, the altered regulation of secretome components, including follistatin-like protein-1, osteoglycin, spondin-2, and cytokine-induced apoptosis inhibitor-1, along with constitutively expressed factors, such as fibulin-2, illustrate dynamic changes in the secretome that take place when differentiation to a specific lineage occurs.

Proliferation of wound derived capillary endothelial cells: young versus aged

The objective of this study was to compare the proliferative potential of wound derived capillary endothelial cells (WCEC) from aged and young rats. Endothelial cells were isolated from subcutaneously implanted sponges in 2- and 24-month-old rats. The identity of the cells as endothelial was confirmed by staining for Ac-LDL uptake. Aged and young WCEC (20,000/well) were stimulated with increasing concentrations of fetal calf serum (0, 2.5, 5, 10 and 15%). The increase in cell number was determined with a Coulter counter. At all serum concentrations, the proliferative capacity of WCEC from aged rats was significantly higher than that of WCEC from young rats.

All-trans retinoic acid (RA) stimulates events in organ-cultured human skin that underlie repair. Adult skin from sun-protected and sun-exposed sites responds in an identical manner to RA while neonatal foreskin responds differently

Adult human skin from a sun-protected site (hip) and from a sun-exposed site (forearm) was maintained in organ culture for 12 d in the presence of a serum-free, growth factor-free basal medium. Cultures were incubated under conditions optimized for keratinocyte growth (i.e., in 0.15 mM extracellular Ca2+) or for fibroblast growth (i.e., in 1.4 mM extracellular Ca2+). Treatment with all-trans retinoic acid (RA) induced histological changes in the organ-cultured skin under both conditions which were similar to the changes seen in intact skin after topical application. These included expansion of the viable portion of the epidermis and activation of cells in the dermis. In sun-damaged skin samples, which were characterized by destruction of normal connective tissue elements and presence of thick, dark-staining elastotic fibers, a zone of healthy connective tissue could be seen immediately below the dermo-epidermal junction. This zone was more prominent in RA-treated organ cultures than in matched controls. Associated with these histological changes was an increase in overall protein and extracellular matrix synthesis. In concomitant studies, it was found that RA treatment enhanced survival and proliferation of adult keratinocytes and adult dermal fibroblasts under both low- and high-Ca2+ conditions. In all of these assays, responses of sun-protected and sun-exposed skin were identical. In contrast, responses of neonatal foreskin to RA were similar to those of adult skin in the presence of low-Ca2+ culture medium, but under conditions of high extracellular Ca2+ RA provided little or no additional stimulus. Together these studies suggest that the ability of RA to enhance repair of sun-damaged skin (documented in previous studies) may reflect its ability to influence the behavior of skin in a manner that is age dependent but independent of sun-exposure status.

Re-expression of senescent markers in deinduced reversibly immortalized cells

We have developed a simian virus 40 (SV40) T-antigen immortalized human cell line, 1MR90-D305.2H4 (IDH4), in which the expression of T-antigen is controlled by the mouse mammary tumor virus (MMTV) promoter and thus regulated by steroids such as dexamethasone. Studies on the regulation of proliferation by T-antigen led to the formulation of a two-stage model for human cell immortalization, in which a mortality stage 1 mechanism (M1) was the target of T-antigen action, and an independent mortality stage 2 mechanism (M2) produced crisis and prevented T-antigen from directly immortalizing cells. Rarely, a cell expressing T-antigen escaped crisis (e.g., M2) and was capable of indefinite proliferation. This model predicted that the deinduction of T-antigen in IDH4 cells would lead to the reexpression of the M1 mechanism, and thus a reexpression of the senescent phenotype. Our study confirms the prediction that, in the absence of steroids, IDH4 cells express a variety of morphological and biochemical markers characteristic of normal senescent human fibroblasts.

Base-exchange and cell growth in 3T6 mouse fibroblasts

Synthesis of phosphatidyl serine by base-exchange and DNA synthesis both declined rapidly in mouse fibroblast cultures upon withdrawal of serum from nutrient medium. Base-exchange returned to control levels within 3 h after the addition of serum, while DNA synthesis lagged by 10 h. Phosphatidyl serine synthesis is thus an early response of 3T6 cells to mitogenic signals.

Effects of ageing on the growth and differentiated function of transfected human thyrocytes

Senescence in primary cultures of mammalian cells is characterised by cessation of growth after a number of cell divisions; this may be associated with loss of some differentiated functions. Recent studies on bovine adrenocortical cells have suggested that expression of simian virus-40 (SV40) early region in these cells may prevent phenotypic losses due to senescence. We report here data on growth and differentiated function of two human thyrocyte cell lines (SGHTL-34 and -45) generated by the transfection of primary thyrocytes with the plasmid pSV3neo which contains the SV40 early region. Growth was assessed by fluorometric DNA estimations and calculation of cell population doubling time; function was assessed by binding studies using 125I-bovine thyrotrophin (TSH) and measurement of cyclic adenosine 3',5'-monophosphate (cAMP) response to stimulation with TSH, forskolin and cholera toxin. After 3-12 months in stable culture there was a gradual increase in the doubling time of both cell lines over a 3-month period (SGHTL-34 cells, early 34.5 +/- 4.5 h, late 301 +/- 111.6 h; SGHTL-45 cells, early 53.4 +/- 4.4 h, late 148.3 +/- 26.3 h; mean +/- SEM). Scatchard analysis demonstrated a loss of the high affinity TSH receptor over the same time period. The increase in cAMP in response to 1000 microU/ml TSH declined until the cells became unresponsive (SGHTL-34 early, cAMP 10.3 +/- 0.7 pmol/well; late, cAMP -0.4 +/- 0.3 pmol/well; SGHTL-45 early, cAMP 11.3 +/- 1.1 pmol/well, late, cAMP 0.3 +/- 0.1 pmol/well). The cAMP responses to forskolin and cholera toxin were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered cellular responsiveness during ageing

The capacity of cells and organisms to respond to external stimuli and to maintain stability in order to survive decreases progressively during ageing. The mitogenic and stimulatory effects of growth factors, hormones and other agents are reduced significantly during cellular ageing. The sensitivity of ageing cells to toxic agents including antibiotics, phorbol esters, radiations and heat shock increases. This failure of homeostasis during cellular ageing does not appear to be due to any quantitative and qualitative defects in the receptor systems. Instead, metabolic defects in the pathways of macromolecular synthesis may be the basis of altered cellular responsiveness during ageing.

Homoeostatic imbalance during cellular ageing: altered responsiveness

The inability of normal cells to maintain themselves for ever is a reflection of homoeostatic imbalance and a progressive failure of maintenance. Ageing cells respond less to growth stimulants whereas they show increased sensitivity to toxic agents including antibiotics, phorbol esters, radiation and other physical stresses. No major quantitative and qualitative defects in the receptor systems have been detected that could explain the reasons for altered responsiveness during ageing. Random metabolic defects in the processes involved in maintaining homoeostasis may be critical for causing homoeostatic imbalance, cellular ageing and death.

Immortalization of primary cells by DNA tumor viruses

Cellular senescence is characterized by a decline in sensitivity to growth factors resulting in cessation of cellular growth. The expression of cellular or viral oncogenes may result in the establishment of cell lines with unlimited proliferative potential ("immortalization"). A variety of viral and cellular oncogenes have been reported to immortalize cells, suggesting that multiple mechanisms may lead to an escape from senescence. Immortalization has been reported to occur as a result of an interaction of viral proteins with cellular suppressor gene products or may result from the elevated expression of "transforming" oncoproteins (such as the polyomavirus middle-t antigen). Here we speculate that a selection for cells with a further decreased probability of cell cycle withdrawal can occur during the growth of cells expressing viral early genes, resulting in a process of tumor progression. Explaining immortalization in terms of mitogenic stimulation due to the expression of viral oncogenes followed by genetic/epigenetic changes may help to explain why lytic DNA viruses have a biological activity which may not be necessary for their life cycle.

Tumor necrosis factor reduces lifespan of human endothelial cells in vitro

Tumor necrosis factor (TNF) is known to regulate the proliferation and function of vascular endothelial cells (ECs). We have examined the effects of TNF on the growth and aging of human ECs of different origins and compared them with those in human normal diploid fibroblasts. The results obtained were as follows: (1) TNF reduces the growth rate and in vitro life span of ECs in both dose- and treatment length-dependent fashions; (2) ECs are significantly more sensitive to TNF than fibroblasts; and (3) the life span shortening effect of TNF on ECs increases as a function of in vitro cell age. These results suggest that the aging of ECs is modified by TNF exposure.

Restoration of the responsiveness to growth factors in senescent cells by an embryonic cell extract

In senescent fibroblast cell cultures which have approached a postmitotic stage in vitro, responsiveness to growth factors is restored upon exposure to an embryonic sheep cell extract. The extract contains molecules below a molecular weight of 1 x 10(5) Da in aqueous solution. Following a transient exposure to the extract, mitotic activity is resumed, and the cells keep dividing over several passages. The target cells which respond to the treatment were identified in a single-cell assay as those that still had the capacity to undergo at least several mitotic divisions before entering the final stage of senescence.

Reversible cellular senescence: implications for immortalization of normal human diploid fibroblasts

IMR-90 normal human diploid fibroblasts, transfected with a steroid inducible mouse mammary tumor virus-driven simian virus 40 T antigen, were carried through crisis to yield an immortal cell line. Growth was dependent on the presence of the inducer (dexamethasone) during both the extended precrisis life span of the cells and after immortalization. After dexamethasone removal, immortal cells divided once or twice and then accumulated in G1. These results are best explained by a two-stage model for cellular senescence. Mortality stage 1 (M1) causes a loss of mitogen responsiveness and arrest near the G1/S interface and can be bypassed or overcome by the cellular DNA synthesis-stimulating activity of T antigen. Mortality stage 2 (M2) is an independent mechanism that is responsible for the failure of cell division during crisis. The inactivation of M2 is a rare event, probably of mutational origin in human cells, independent of or only indirectly related to the expression of T antigen. Under this hypothesis, T-antigen-immortalized cells contain an active but bypassed M1 mechanism and an inactivated M2 mechanism. These cells are dependent on the continued expression of T antigen for the maintenance of immortality for the same reason that precrisis cells are dependent on T antigen for growth: both contain an active M1 mechanism.

Coordinate control of growth arrest states in normal human diploid fibroblasts: effect of cloned SV40 tumor antigen genes

The growth arrest states of quiescence and senescence in normal human diploid fibroblasts (HDF) are related but distinct phenomena. In an effort to (1) understand the extent to which arrest in the quiescent state and arrest in the senescent state share common regulatory mechanisms, and (2) test our hypothesis that when the quiescent phenotype is altered in HDF, then the senescent phenotype is likewise altered, we have transfected HDF with cloned SV40 tumor antigen genes. Introduction of the tumor antigen genes results in a loss of the ability to enter both the quiescent arrest state and the senescent arrest state but does not immortalize the cells or create significant aneuploidy.

Quantitation of the frequency of immortalization of normal human diploid fibroblasts by SV40 large T-antigen

The mechanism by which SV40 large T-antigen immortalizes human lung fibroblasts is not yet understood, and the frequency with which immortalization occurs is unknown. Here we report detailed studies of the kinetics of immortalization. Approximately 20-50% of individual T-antigen transfected clones of IMR-90 human lung fibroblasts are able to immortalize. The failure of some clones to immortalize is consistent with the hypothesis that in some cells the aneuploidy induced by T-antigen produces extra copies of the chromosome containing a factor that must be inactivated before immortalization occurs. Within immortalization-competent clones, the frequency of immortalization is about 3 X 10(-7). This frequency is consistent with a mutational mechanism for the inactivation of the factor that causes crisis in T-antigen expressing cells.

Reversible cellular senescence: implications for immortalization of normal human diploid fibroblasts

IMR-90 normal human diploid fibroblasts, transfected with a steroid inducible mouse mammary tumor virus-driven simian virus 40 T antigen, were carried through crisis to yield an immortal cell line. Growth was dependent on the presence of the inducer (dexamethasone) during both the extended precrisis life span of the cells and after immortalization. After dexamethasone removal, immortal cells divided once or twice and then accumulated in G1. These results are best explained by a two-stage model for cellular senescence. Mortality stage 1 (M1) causes a loss of mitogen responsiveness and arrest near the G1/S interface and can be bypassed or overcome by the cellular DNA synthesis-stimulating activity of T antigen. Mortality stage 2 (M2) is an independent mechanism that is responsible for the failure of cell division during crisis. The inactivation of M2 is a rare event, probably of mutational origin in human cells, independent of or only indirectly related to the expression of T antigen. Under this hypothesis, T-antigen-immortalized cells contain an active but bypassed M1 mechanism and an inactivated M2 mechanism. These cells are dependent on the continued expression of T antigen for the maintenance of immortality for the same reason that precrisis cells are dependent on T antigen for growth: both contain an active M1 mechanism.

An extract of bovine thymus stimulates human keratinocyte growth in vitro

An extract prepared from newborn calf thymus stimulated proliferation of human keratinocytes cultured from newborn foreskins and from skin biopsies of 26 adult volunteers aged 19 to 70 years. Growth over the 7-day assay period in the basal medium was age-dependent, with newborn cultures achieving a 10-fold increase in cell number over seeding density, old adult cultures barely maintaining their seeding density and young adult cultures intermediate in proliferative capacity. Maximally stimulatory extract concentration was 5-fold higher for newborn than for adult keratinocytes, with adult cultures experiencing toxicity at doses still growth-promoting for newborn cultures. At optimal extract concentration the maximal average increase in cell yield (66.3% for newborn, 53.6% for young adult, and 18.1% for old) indicated decreased mitogen responsiveness or increased inhibitor sensitivity with increasing donor age. Stimulation of cholera toxin-treated cultures was equally high, ranging from 39.4% to 145.9%, suggesting that the extract acts through a cyclic AMP-independent pathway. Thymic extract did not increase colony forming efficiency. Our findings provide further support for the concept of functional interactions between the skin and the immune system, in addition to the recognized morphologic similarities between thymic cells and keratinocytes. Furthermore, these data confirm earlier findings of an inverse relationship between mitogen responsiveness and donor age for cultured cells.

The aging of the endocrine pancreas of the rat. I. Parameters of cell proliferation

Morphometrical analysis of the endocrine pancreas of senile 30-month-old rats revealed that the volume density as well as the numeric density of islets of Langerhans were much lower than in 24-month-old rats, which coincided with a much higher percentage of pycnotic nuclei in islet cells. The proportion and localization of the different categories of endocrine cells (A, B, D and PP) remained however unchanged with aging. The apparent problem of cell renewal observed in vivo in the very old age was detected earlier in vitro by tritiated thymidine incorporation. Such experiments showed that 24-month-old islet cells had a decreased labelling index when compared to 3-month-old cells. The proliferation capacity of the old cells could be partially increased by changing the serum concentration or type. Similarly as being more sensitive to serum factors, these cells underwent also more pronounced negative influence of high oxygen pressure on replication. A stereological analysis of the ultrastructure of non-degenerated B-cell nuclei revealed that with age, the relative volume of the condensed chromatin increased progressively at the expense of the dispersed form. This suggests that the still functioning senile B-cells could reduce their transcriptional activity.

Autocrine growth stimulation of human keratinocytes by epidermal cell-derived thymocyte-activating factor: implications for skin aging

The monocyte-derived cytokine interleukin-1 (IL-1) has growth-promoting activity for a variety of cell types, including lymphocytes and fibroblasts. We have previously shown that the epidermal cell-derived thymocyte-activating factor (ETAF) strongly resembles IL-1 in terms of biological, biochemical, and molecular biological properties. Because some lymphokines are known ot alter epidermal cell growth and differentiation and because cultured epidermal keratinocytes are capable of autocrine growth stimulation in vitro through "conditioning" of their culture medium, we sought to evaluate the effect of ETAF on keratinocyte growth. While there was marked donor variability in the responsiveness of keratinocytes to ETAF, partially purified preparations of ETAF showed substantial ability to stimulate the growth of keratinocytes, particularly those of newborn donors. In addition, in conditioned media there appeared to be activities distinct from ETAF that also promoted keratinocyte growth. Keratinocytes in serum-free medium secreted large amounts of ETAF, as reported previously, and keratinocyte cultures derived from newborn donors secreted significantly more than did those derived from adult donors. These results are consistent with an autocrine growth regulatory role of ETAF in human epidermis and with an age-associated loss of this phenomenon.

Differences in growth factor sensitivity between individual 3T3 cells arise at high frequency: possible relevance to cell senescence

At low serum concentrations (3% or less), individual Swiss 3T3 cells display marked heterogeneity in proliferative capacity. Here we show that this heterogeneity arises at extremely high frequency within a clone, often with sister cells showing considerable differences in capacity for further proliferation. The heterogeneity is unlikely to be due to genetic instability or mutation. Instead, it appears to reflect physiological differences between cells in their requirement for serum growth factors. It is suggested that these differences arise because cells are unable to sustain production, at low growth factor concentrations, of some rare component which is itself required for growth factor action. We believe that the generation of heterogeneity in 3T3 cells has much in common with the phenomenon of senescence in diploid cells.

Cellular senescence revisited: a review

The field of cellular senescence (cytogerontology) is reviewed. The historical precedence for investigation in this field is summarized, and placed in the context of more recent studies of the regulation of cellular proliferation and differentiation. The now-classical embryonic lung fibroblast model is compared to models utilizing other cell types as well as cells from donors of different ages and phenotypes. Modulation of cellular senescence by growth factors, hormones, and genetic manipulation is contrasted, but newer studies in oncogene involvement are omitted. A current consensus would include the view that the life span of normal diploid cells in culture is limited, is under genetic control, and is capable of being modified. Finally, embryonic cells aging in vitro share certain characteristics with early passage cells derived from donors of increasing age.

Membrane-associated inhibitor of DNA synthesis in senescent human diploid fibroblasts: characterization and comparison to quiescent cell inhibitor

Cell membranes prepared from senescent human diploid fibroblasts (HDF) inhibited entry into S phase by 35% when added to the medium of replicating young HDF. This membrane-associated inhibitory activity was (i) sensitive to trypsin, heat, and periodate, which suggests that the inhibitor is a glycoprotein, and (ii) not able to inhibit DNA synthesis in simian virus 40-transformed HDF, which indicates that not all types of cells are sensitive to this inhibitor. Quiescent young HDF also have a surface membrane-associated inhibitor of DNA synthesis. A comparison of the senescent HDF and quiescent HDF inhibitor activities indicates that they may have the same chemical and physical nature and the same specific activity, but their regulation is different. The inhibitory activity of quiescent young HDF is abolished within 20 hr after refeeding with fresh serum-containing medium, whereas that of senescent HDF remains unchanged. Quiescent old HDF (two or three population doublings remaining) exhibit an intermediate response to serum with approximately two-thirds of the inhibitory activity abolished. The fraction of cells in S phase at 20-24 hr post-stimulation (37% in young HDF, 24% in old HDF, and 0% in senescent HDF) is inversely proportional to inhibitor levels. This suggests that inability to neutralize the inhibitory activity in response to serum stimulation could be involved in the inability of senescent HDF to enter S phase. Disappearance of the inhibitory activity from quiescent young HDF occurs late in G1 phase. Thus, the inhibitor may play a role in determining the length of the G0 to S phase transition in these cells.

Growth factor responsiveness declines during adulthood for human skin-derived cells

Keratinocytes and fibroblasts were obtained from upper arm biopsies of young (22-27 years) and old (60-82 years) adult donors. Keratinocytes were grown in serum-free medium containing variable quantities of either epidermal growth factor (EGF) or a bovine hypothalamic extract known to contain keratinocyte growth factor (KGF). Fibroblasts were grown in serum-free medium containing variable quantities of EGF or insulin. Paired keratinocyte cultures were plated in serum-free medium containing 20% newborn keratinocyte-conditioned medium (NM) or 20% control conditioned medium (CM). Newborn foreskin keratinocytes were plated in 20% conditioned media derived from newborn, young adult or old adult keratinocyte cultures. In spite of large inter-donor variability, keratinocyte growth significantly decreased with age (0.05 greater than P greater than 0.01). Cell yield at 7 days showed an 8-fold increase for young adults over the KGF dose range treated, but only a 4-fold increase for old adults. Young adult cells in varying concentrations of EGF achieved 3-fold to 5-fold higher densities than old, although EGF was not stimulatory for either adult age group. Donor age-associated loss of growth factor responsiveness was confirmed with dermal fibroblasts derived from the same biopsies. Newborn but not adult keratinocytes were stimulated by NM, while newborn cells were not stimulated by either young or old adult conditioned media (YM or OM). An epidermal proliferation index, incorporating both donor cell yield and cell yield of newborn cells in donor conditioned medium, was significantly different (P less than 0.01) for newborn vs. young or old adult cells. Our findings confirm that a decreased proliferative capacity is measurable within adulthood, and suggest that this decrease may be due to a reduced ability to synthesize or respond to mitogens, including autocrine factors.

The suppression of endogenous protein degradation by fractions of foetal calf serum: dialysed serum is less able to suppress degradation in aged cells

We have studied the effect of various fractions of foetal bovine serum upon the endogenous degradation of long labelled proteins in cultured MRC5 cells, and upon other cellular functions. Only heat-inactivated serum was capable of suppressing protein degradation to a similar extent to complete serum. Acid-treated and delipidized sera were moderately effective. Albumin on its own was able to replace 40 per cent of the effect of serum, indicating the exogenous protein might compete with endogenous protein for degradation in lysosomes. Albumin was not capable of supporting DNA synthesis. Dialysed serum showed an age-related effect suppressing protein degradation to a lesser extent and being less effective in supporting DNA synthesis or cellular proliferation in aged cells. All the effects noted were related to lysosomal protein degradation. Serum diffusate did not suppress protein degradation.

Distinction of G0 cells from senescent cells in cultures of non-cycling human fetal lung fibroblasts by anti-MAP-1 monoclonal antibody staining

On staining with a monoclonal antibody raised against microtubule-associated protein-1 (MAP-1), dot-like structures were seen in the nuclei of interphase cells, but not in those of non-cycling G0-arrested cells. Dots were also not seen in the nuclei of non-cycling senescent human cells (IMR-90). A SV40-DNA-transformed subline of IMR-90 with a limited growth potential showed progressive decrease of cells with nuclei containing dots in the final stage of their lifespan. The dots appeared in G0-arrested IMR-90 cells when these cells were incubated in medium of high osmotic pressure for 3 min. In contrast, no dots appeared in senescent cells or X-ray-irradiated young cells when they were incubated in medium of high osmotic pressure. Thus irreversibly non-cycling cells could be distinguished from G0-phase cells on the level of whole cultures. The results suggest that senescent cells lose their division potential by entering an irreversible cell-cycle stage differing from G0.

SV40-transformed human fibroblasts: evidence for cellular aging in pre-crisis cells

Pre-crisis SV40-transformed human diploid fibroblast (HDF) cultures have a finite proliferative lifespan, but they do not enter a viable senescent state at end of lifespan. Little is known about either the mechanism for this finite lifespan in SV40-transformed HDF or its relationship to finite lifespan in normal HDF. Recently we proposed that in normal HDF the phenomena of finite lifespan and arrest in a viable senescent state depend on two separate processes: 1) an age-related decrease in the ability of the cells to recognize or respond to serum and/or other mitogens such that the cells become functionally mitogen-deprived at the end of lifespan; and 2) the ability of the cells to enter a viable, G1-arrested state whenever they experience mitogen deprivation. In this paper, data are presented that suggest that pre-crisis SV40-transformed HDF retain the first process described above, but lack the second process. It is shown that SV40-transformed HDF have a progressively decreasing ability to respond to serum as they age, but they continue to traverse the cell cycle at the end of lifespan. Concomitantly, the rate of cell death increases steadily toward the end of lifespan, thereby causing the total population to cease growing and ultimately to decline. Previous studies have shown that when SV40-transformed HDF are environmentally serum deprived, they likewise exhibit continued cell cycle traverse coupled with increased cell death. Thus, these results support the hypothesis that pre-crisis SV40-transformed HDF still undergo the same aging process as do normal HDF, but they end their lifespan in crisis rather than in the normal G1-arrested senescent state because they have lost their ability to enter a viable, G1-arrested state in response to mitogen deprivation.

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.

Changes in protein synthesis and breakdown rates and responsiveness to growth factors with ageing in human lung fibroblasts

The effects of insulin, epidermal growth factor, insulin-like growth factor-2 and fetal bovine serum on protein synthesis and protein breakdown have been measured in mid-passage and senescent cultures of human diploid lung fibroblasts. Each of the individual growth factors was a potent inhibitor of protein breakdown with no difference in either the maximum response or sensitivity evident between senescent cells and mid-passage cultures. Binding of 125I-labelled epidermal growth factor per mg of cell protein similarly showed no difference between senescent and confluent mid-passage fibroblasts, although sparse mid-passage cells bound more of the ligand. These results indicate normal binding and normal responsiveness to growth factors in senescent cultures. However, rates of protein synthesis are higher in confluent mid-passage cells and especially so in sparse mid-passage cells than in senescent cells of intermediate density. Furthermore, senescent cells differ from either growth state of mid-passage cells because protein synthesis in aged cells is much less responsive to any of the growth factors or to fetal bovine serum. It is suggested from these results that the reduced ability of serum or growth factors to initiate DNA synthesis or growth in ageing cells may be a consequence of an unresponsive protein synthesis pathway rather than a generalised defect in growth factor action.

Relationship of finite proliferative lifespan, senescence, and quiescence in human cells

Cell hybrids were formed between human diploid fibroblasts (HDF) and carcinogen-transformed HDF to determine the relationship among: (1) finite proliferative lifespan, which we define as an age-related failure of a population to achieve one population doubling in 4 weeks; (2) arrest in a senescent state, which we define as cessation of DNA synthesis in a viable culture that is at the end of its lifespan by the above definition; and (3) arrest in a quiescent state, which we define as cessation of DNA synthesis in a young culture that is crowded or mitogen-deprived. HDF express all three of these phenotypes, which we have abbreviated FPL+, S+, and Q+, respectively. Carcinogen-transformed HDF are transformed to immortality (FPL-) and inability to achieve quiescence (Q-). They have no S phenotype because, by definition, this phenotype only exists in FPL+ cells. Fusion of FPL+, Q+, S+ HDF X FPL-, Q- carcinogen-transformed HDF produced hybrid clones that were FPL+, Q-, and S-, where the S- phenotype means that individual cells continued to synthesize DNA in cultures that had reached the end of their lifespan by our definition. These results are consistent with our hypothesis that senescent HDF and quiescent HDF may share a common mechanism for arrest in G1 phase. We have suggested that this could occur if the aging mechanism that is responsible for the FPL+ phenotype is a progressive decrease in the ability of cells to recognize or respond to mitogenic growth factors. If so, then cells would become physiologically mitogen-deprived at the end of their lifespan, which would cause them to arrest in the senescent state by the same mechanism that causes young cells to arrest in the quiescent state when they are mitogen-deprived. This hypothesis predicts that the FPL+ phenotype can be separated from the S+ phenotype--i.e., FPL+ cells can be S+ or S- --and that the Q and S phenotypes are linked--i.e., FPL+ cells are either Q+ and S+ or Q- and S-. Both these predictions are supported by the present data.

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.

Apparent heterogeneity in the response of quiescent swiss 3T3 cells to serum growth factors: implications for the transition probability model and parallels with "cellular senescence" and "competence"

When subconfluent, Swiss 3T3 cells made quiescent by serum deprivation are stimulated with low concentrations of serum (ca. 1%), only a proportion of them (roughly 50%) enter S phase despite daily replacement with fresh, low-serum medium. The cells that fail to enter S phase are not incapable of doing so, since most of them initiate DNA synthesis after transfer to 10% serum. It would appear that individual cells vary in their growth factor requirements. Using time-lapse cinemicroscopy a few of the cells that respond to low serum were seen to give rise to several generations of progeny, while the majority of cells failed to divide at all, or divided once at most. Despite this, differences between cells in growth factor requirements do not seem to be heritable in the long term, since attempts to enrich for responding cells by prolonged culture in 1% serum have been unsuccessful. Rather, it would appear that the capacity to respond to low serum is an unstable property lost after a few generations in low serum. The loss of responsiveness shows parallels with "cellular senescence" and could conceivably result from decay of the platelet-derived growth factor-induced state of "competence." But regardless of why some cells respond to low serum while others do not, it is clear that the kinetics of entry into S phase after serum stimulation of quiescent 3T3 cells are not strictly first-order, since the labelling index plateaus after roughly 3 days at values substantially below 100%. As such, the kinetics, though not contradicting the transition probability model, cannot be taken to support it as was previously thought.

Differential recovery from potentially lethal damage in normal human lung fibroblasts after irradiation with 60Co gamma-rays and accelerated N-ion beam

PLD recovery after irradiation with accelerated N-ion was examined and compared with that after irradiation with 60Co gamma-rays in normal human lung fibroblasts (IMR-90). No shoulder region was observed in the survival curve of the cells after N-ion irradiation. Ratios of D0 values before and after a 6-hour incubation in plateau phase were 1.1 and 1.8 for N-ion irradiation and gamma-ray irradiation, respectively. The results show that recovery after irradiation with high-LET radiation is slow and much less than after low-LET irradiation.

A quantitative analysis of the aging of human glial cells in culture

The kinetics of aging of normal human diploid brain cells in culture have been determined using the miniclone technique in which cells are cloned in the presence of a large number of other cells. The miniclone technique records the behaviour of every viable cell in the sample, not merely those cells capable of forming visible clones. This technique permits the direct measurement of the reproductive potential of individual cells growing in bulk culture and of the dispersion of the sizes of colonies generated by dividing cells. The fraction of cells that are able to divide declines smoothly and continuously from the beginning of in vitro cultures of human glial cells. There is a broad distribution of colony sizes; even at the earliest passages there are significant numbers of small colonies. With increasing age of the culture there is a shift in the distribution, so that fewer large colonies and more small colonies occur. The distribution of intermitotic times is almost identical in young and middle-aged cultures. Our data seem to exclude quite positively any description in terms of a catastrophe or any abrupt change in the population. On the contrary, the decline in reproductive potential may be described adequately either as a linear change with time, or as predicted by the mortality theory of Shall and Stein (1979), in which the single constant, gamma, describes the change in reproductive potential over the entire lifetime.

In vitro assessment of keratinocyte aging

In vitro aging models are based on the observation that normal cells in culture have a finite lifespan and eventually cease to proliferate under conditions that initially support excellent growth. Recent assessment of the aging process in keratinocytes, made possible by improved tissue-culture techniques, have confirmed prior findings with fetal and adult fibroblasts and have permitted investigation into the mechanism of in vitro senescence. Early-passage newborn human keratinocytes maintained in a serum-free system were found to proliferate more rapidly than early-passage adult keratinocytes maintained under identical conditions, and they were also found to have far steeper dose-response curves for a potent hypothalamus-derived mitogen keratinocyte growth factor (KGF), as well as for KGF/EGF in combination, with a more than 200-fold increase in cell number, total protein, and colony size over the tested range of concentrations, as opposed to a less than 75-fold increase for adult keratinocytes in these parameters. These results support the hypothesis that the age-associated decrease for keratinocyte proliferation in vitro may be due to progressive loss of mitogenic responsiveness. Unrecognized changes in proliferative rate and growth-factor requirements related to age of the tissue donor may complicate interpretation of studies addressing other aspects of keratinocyte biology.

Replicative activity and actinomycin binding in mouse diploid fibroblasts (in vitro ageing)

Populations of embryonic mouse fibroblasts undergo 10 +/- 2 doublings in vitro prior to cessation of growth. We have studied various properties of the DNA of such cells as they undergo this process of in vitro ageing. Following a 1-h pulse with [3H]thymidine the labelling of growing cell populations decreases progressively with serial subcultivation. At early passage levels, the decrease in labelling between passages is rapid, but after about five passages the decline is much slower. Following a long pulse with [3H]thymidine (up to 4 days), up to 50% of the cells in the final passage become labelled. The binding of [3H]actinomycin to nuclei decreases progressively during serial subcultivation. Under conditions of quiescence, induced by serum deprivation, the cells withdraw from the S-phase. Feulgen cytophotometry reveals a wide spectrum of cellular DNA contents in terminal cultures, with 38% of cells possessing more DNA than equivalent early passage cells. Under these conditions, 40% of the fibroblasts bind less actinomycin than any early passage cells. Neither variations in DNA amount nor differences in cell-cycle phases can explain these alterations, which are thought to be related to age-dependent changes in chromatin condensation.