Effects of serum from rabbits of various ages on cell proliferation

Inhibitory effects of human serum on human fetal skin fibroblast migration: migration-inhibitory activity and substances in serum, and its age-related changes

In order to clarify the environmental factors modulating cell migration, we investigated the effects of human serum on cell migration, and found that serum from adult donors strongly (by 48%) suppressed the migration of human fetal skin fibroblasts into a denuded area in a cell monolayer. Human serum from old donors inhibited cell migration more strongly than that from adult donors. Next, we investigated the properties of migration-inhibitory activity of human serum and serum proteins in order to identify migration-inhibitory substances. Human serum from adult donors strongly suppressed the migration of human fetal skin fibroblasts, although it stimulated cell proliferation more strongly than fetal bovine serum (FBS), indicating that the inhibitory effects of human serum on cell migration was not due to its toxic effects. The inhibition of cell migration by human serum was concentration dependent. It was demonstrated that the inhibition did not depend on the inhibitory effects of human serum on collagen synthesis. The migration-inhibitory activity was seen in fractions over 100 kDa, as determined by an ultrafiltration membrane, and no inhibitory activity was observed in fractions under 100 kDa. On the other hand, it was not detected either in fractions over 100 kDa or under 100 kDa in FBS. Among the over 100 kDa human serum proteins examined, gamma-globulin, alpha2-macroglobulin, and low density lipoprotein (LDL) suppressed fibroblast migration in a concentration-dependent manner. However, among the three, cell migration-inhibiting activity of gamma-globulin almost disappeared when cell migration was conducted in 10% FBS-supplemented medium. These results indicated that alplha2-macroglobulin and LDL were candidate substances for cell migration-inhibiting activity in human serum.

Ups and downs of aging studies in vitro: the crooked path of science

Different approaches using cell culture techniques to study the biology of aging are critically described. Most of the studies concerned the relationship between cell division potential and aging. The growth potential of cells is fundamental for aging of the organism, since it relates to phenomena such as the regeneration of tissues, wound healing, the immune response, and stem cell renewal. Unfortunately many experiments were misinterpreted disregarding the physiology of the mammalian organism. The terminal postmitotic cell, on which most research has been concentrated, seems irrelevant for aging of the organism. Nevertheless, some experiments yielded important contributions to the understanding of the biology of cell division. Future research should ascertain such interesting suggestions as the terminal differentiation hypothesis of the human fibroblast life cycle. It is important to elucidate the significance of the increased number of postmitotic cells in pathological processes. A neglected area should be further explored: the relationships between structural modifications of the cell, decreased probability of activating energy barriers, and decline of the division potential.

Effects of aging and dietary restriction on activity of monkey serum in promoting fibroblast migration

In order to determine whether serum modified cellular aging in vivo, we previously studied the effects of serum from various mammals of different ages on cell functions such as proliferation and migration, and reported that cell migration was more greatly inhibited by serum from old donors than cell proliferation [1]. Moreover, since dietary restriction has been reported to extend lifespan and slow the aging rate of some animals [2], we wondered whether sera from dietary restricted and control monkeys of various ages might exhibit reduced aging effects on cell migration. When serum from young adult (3-5 years old) monkeys was added to plain medium, the migration of human fetal skin fibroblasts was very strongly inhibited compared to FBS. Surprisingly, sera from adult (6-11 years old) and old (more than 18 years old) monkeys caused significantly less migration-inhibitory activity than serum from young adult monkeys although sera from adult and old monkeys were much more inhibitory to cell migration than FBS. Dietary restriction only caused marginal effects on serum migration-promoting activity in a few monkey groups. The inhibition of cell migration caused by monkey serum was not brought about by cytotoxic effects since monkey serum stimulated cell proliferation as well as fetal bovine serum. These results indicate that the effects of aging on monkey serum migration-promoting activity are much more pronounced than those of dietary restriction.

Species difference in the resistibility of embryonic fibroblasts against oxygen-induced growth inhibition

The growth of fibroblasts, which were isolated from human, rabbit, rat, mouse, and chick embryos, was inhibited partially under 50% oxygen and nearly completely under 95% oxygen. There was species difference in the resistivity of these cells against oxygen-induced growth inhibition. The extent of the resistivity was in the following order: chick cells > rat cells > human cells > rabbit cells approximately mouse cells. The order of their ability to recover from oxygen-induced growth inhibition was similar to the above order of species. There was also species difference in their antioxidant enzyme activities, including superoxide dismutase, catalase, and glutathione peroxidase activities, and their reduced glutathione concentration. Chick cells, having the highest resistivity against oxygen-induced growth inhibition, were at the lowest activity levels of antioxidant enzymes and at the highest concentration level of reduced glutathione. The species difference in resistivity against oxygen-induced growth inhibition seems to depend on the reduced glutathione concentration, but not on the antioxidant enzyme activities.

Age-related changes in the mitogenic activity of heparin-binding growth factors in rat sera

Sera from rats of either sex and different ages were examined for their ability to stimulate DNA synthesis in BALB/c 3T3 cells. The activity levels of sera from male and female rats were almost the same, with age-related changes in activity also being quite similar. Activity was considerably higher in infant rats (1-month-old), but then, at a young age (6-7 months), decreased drastically for male rats, but not significantly for female rats. It increased again in middle-aged rats (12-13 months old) and was maintained at the same level toward old age (24-26 months old) for both sexes. In order to determine what kinds of growth factors were responsible for these changes, we carried out heparin affinity chromatography on the sera of male rats. Four peaks were obtained for all sera, with individual peaks exhibiting specific age-related changes in activity. Among them a peak which was eluted at 1.1 M NaCl had very high activity. It showed a similar age-related change to that of the whole sera, except for a significant increase at old age, and the factor(s) included in the peak was found to be derived from platelets. These results suggested that the factor(s) in the peak was responsible for maintaining serum mitogenic activity at an old age. The experiments undertaken to characterize this factor suggested that it is a novel one.

Effects of serum from human subjects of different ages on migration in vitro of human fibroblasts

A study was carried out to determine whether human serum from older subjects inhibited cell migration. Sera of both sexes from subjects in their 60s (60-64 years) tended to be more inhibitory (8-14%) to the migration of human fetal lung fibroblasts, TIG-1, than serum from subjects in their 20s (20-29 years). In the case of females, the effects of serum on cell migration were significantly (P less than 0.05) different between the younger and older groups. Next, cell migration-stimulatory activity of serum was measured using human skin fibroblasts from young adult (age 21) and elderly (age 65) donors. The results were similar to those obtained with TIG-1 cells. However, the cell migration-stimulatory activity of serum was not significantly different between the two age groups. A study on the effects of concentration of human serum on the migration of TIG-1 cells showed that cell migration-stimulatory activity of serum declined linearly with increasing concentrations of sera from subjects in their teens (16-19 years) and 50s (50-59 years), and was the same between the two age groups. These results imply that substance(s) inhibitory to cell migration may not have accumulated in serum during the ageing process in humans, although human serum contained substance(s) inhibitory to cell migration.

Effects of serum from human subjects of various ages on proliferation of human lung and skin fibroblasts

We carried out a study to determine whether serum from old human subjects inhibited cell proliferation. The results showed that serum from old subjects of either sex did not greatly inhibit the proliferation of human fetal lung fibroblast TIG-1 cells, even when serum from subjects in their 80s was used. The same results were obtained when the effects of serum on cell proliferation were examined up to a serum concentration of 50%. It was also found that serum from old subjects did not inhibit proliferation of human skin fibroblasts from a young adult to any greater degree than serum from young adult subjects, and that serum from young adult subjects did not stimulate proliferation of skin fibroblasts from an elderly donor to any greater degree than serum from old subjects.

Effects of serum collected from rats of different ages on in vitro cell proliferation

It has been reported by Carrel and his co-workers that serum from old hens inhibits cell growth in culture. However, as we had previously demonstrated contradictory results using serum from old rabbits, we examined whether serum from old rats would also show strong induction of cell proliferation. Sera from young and adult rats of either sex strongly stimulated the growth of rat fetal skin fibroblasts and human fetal lung fibroblasts (TIG-1). Sera of old female and male rats (24-29 months old) produced much greater fluctuations in growth-stimulatory activity than sera from young animals. Most samples of serum from old rats stimulated the growth of TIG-1 cells, as did fetal bovine serum and samples from younger rats, even when a higher concentration of serum (up to 50%) was used. On the other hand, a small proportion of samples repressed the growth of the cells. A study on the effects of serial mixtures of both different types of serum samples from old rats on cell growth suggested that this minor proportion of serum samples contain a large amount of inhibitory factor(s). The cell growth-stimulatory activity of serum did not correlate with the total protein and albumin concentrations, albumin/globulin ratio, and the levels of lipid peroxide in the sample. These results therefore seemed to imply that serum induced a striking increase in the heterogeneity of cell growth stimulatory activity with age, although most samples of serum from old rats of either sex stimulated cell proliferation as effectively as samples from younger rats. The biological significance of the small proportion of serum samples from old rats which do inhibit cell proliferation was discussed.

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.