Contributions made by the studies of cells in vitro for understanding of the mechanisms of aging

Inverted skin changes induced by estrogen and estrogen/glucocorticoid on aging dermis

To evaluate hormone replacement therapy effects at the peripheral level, the present trial explored the oral effects of mestranol (80 micrograms/day for 10 days) and mestranol plus paramethasone (80 micrograms + 6 mg/day for 10 days) on the skin of postmenopausal women. This double-blind study included 13 patients. Skin biopsies were obtained from the thigh area by a single punch, 5 mm in diameter, before and after treatment, and the sections, six per sample, were micrometrically evaluated. Various features of the epidermis and dermis layers were stained using the hematoxylin and eosin, Masson, Verhoeff's and Gomori techniques. Statistically significant changes were found in the papillar dermis thickness; mestranol reduced it and mestranol plus paramethasone increased it. The current results encourage widening these observations of the possible advantage of this estrogen/glucocorticoid combination, in order to alleviate the cellular degenerative process.

Screening for genetic predisposition to mutagens in cancer patients

Both genetic and environmental factors are known to play an important role in the development of cancer. To determine whether, among individuals who develop cancers, some may have been more susceptible to the mutagenic effects of environmental agents, skin biopsies were taken from 79 cancer patients with different common types of cancers (e.g., lung, breast, bladder, colon, cervix, ovary, brain, vocal cord, uterus, skin, testis, stomach, basal cell carcinoma, leukemia, etc.). Fibroblast cultures have been established from skin explants from nearly all of the patients. The sensitivity of some of these cells as well as a number of other fibroblast strains established from "clinically normal" individuals to a battery of mutagenic agents (e.g., ethylmethane sulfonate, methylmethane sulfonate, ethidium bromide, actinomycin D, mitomycin C, bleomycin, camptothecin), which induce different kinds of DNA damage was examined. For the control group of fibroblasts, a normal range of toxicity for all of the above agents have been established. In contrast to other mutagens for which sensitivity of all of the control cell strains lay within a narrow range, large and interesting differences in sensitivity were observed for ethidium bromide. The fibroblast strains established from fetal tissue were found to be highly resistant to ethidium bromide, whereas fibroblasts from two clinically normal persons exhibited greatly enhanced sensitivity to this agent. The genetic or biochemical basis of increased sensitivity or resistance to ethidium bromide remains to be determined. The sensitivity of cells from 28 cancer patients to a number of the mutagenic agents was also examined. Most of these strains exhibited normal range of sensitivity to the mutagens; however, a few showed small but noticeable differences in sensitivity to specific agents. The fibroblast strains from cancer patients provide a useful resource to examine the genetic and metabolic factors that may be important determinants in cancer susceptibility.

Inhibition of proliferation in 8-week-old mdx mouse muscle fibroblasts in vitro

Our purpose is to understand why mdx muscle does not show the progressive degeneration observed in human Duchenne muscular dystrophy (DMD) muscle. In the mouse, the regenerative process compensates for the necrosis of the muscle fibers, particularly during the acute phase of the disease (5-9 weeks). In DMD muscle, there is a gradual failure of the regenerative process and the muscle fibers are replaced by connective and fatty tissue. We propose that distinct properties of mdx and DMD muscle fibroblasts could be one of the reasons for the differences between the mdx and DMD phenotypes. We found that fibroblasts taken from human DMD and control muscle had similar in vitro proliferative capacities. The proliferation rate of mouse muscle fibroblasts decreased during the acute phase of the disease, and inhibition was complete in fibroblasts from 8-week-old mdx mice. Moreover, the medium conditioned by these cells inhibited fibroblast proliferation. The effect was specific for fibroblasts, since this conditioned medium stimulated myoblast proliferation, as did control fibroblast-conditioned medium. These results suggest that 8-week-old mdx mouse muscle fibroblasts produce an inhibitor of their own proliferation and a growth factor specific for myoblasts in vitro. If these factors are secreted in vivo, the growth inhibitory factory may stop fibroblast proliferation whereas the mitogenic activity could stimulate satellite cell proliferation, thus favouring muscle regeneration.

Age-related alterations in collagen and total protein metabolism determined in cultured rat dermal fibroblasts: age-related trends parallel those observed in rat skin in vivo

The cultured fibroblast has been extensively used as a model system to study aging. However, few studies have examined the veracity of observations obtained in cultured fibroblasts aged in vitro to those made in animal tissues in vivo. This paper compares age-related alterations in collagen metabolism measured in cultured cells with previously reported results in the aging rat (Mays et al. (1991) Biochem. J. 276, 307-313). Age-related changes in collagen synthesis in rat skin fibroblasts in vitro over 30 population doublings were determined based on the production of hydroxy-[14C]proline. Degradation of newly synthesized collagen was based on the appearance of free hydroxy-[14C]proline in the culture system. Total protein synthesis rates were based on the incorporation of [14C]proline into proteins. In vitro rates of collagen synthesis decreased 5-fold over 30 population doublings (P < 0.05). Degradation of newly synthesized collagen increased from 33.0 +/- 0.8% (n = 4, SEM) to 45.2 +/- 1.1% (n = 4; P < 0.05) over the same period, with a maximum after 25 population doublings of 55.8 +/- 1.1% (n = 4). Total protein synthesis rates decreased by one-half over 30 population doublings (P < 0.05). The results indicated that collagen production decreased as cells aged in vitro and that this was due to both changes in synthesis and degradation. The results demonstrate that age-related alterations in collagen and total protein metabolism of skin fibroblasts in culture were similar to those reported previously for skin in vivo, suggesting that for studies of these processes, fibroblasts in culture provide an appropriate model.

Accelerated aging of dermal fibroblast-like cells from senescence-accelerated mouse (SAM). 1. Acceleration of population aging in vitro

Fibroblast-like cells were isolated from the senescence accelerated mouse (SAM) and cultured, after which evidence of accelerated senescence was sought. Fibroblast-like cell lines were established from the dorsal dermis of neonate mice of both the accelerated senescence-prone strain, SAMP11 and the accelerated senescence-resistant strain, SAMR1. All cell lines from both strains showed a crisis in growth and were immortalized. At crisis, all cultures were composed of morphologically characteristic senescent cells. However, in cell lines from SAMP11, this change was more rapid and at earlier population doublings (PDs) than seen in cell lines from SAMR1. Crises (SAMP11; SAMR1) were also operationally taken to be the point of the least change in PDs (11.2 +/- 1.1; 15.4 +/- 0.5 PDs), the least saturation density (11.3 +/- 0.8; 19.1 +/- 2.6 PDs), and the longest population doubling time (10.1 +/- 0.8; 14.2 +/- 0.6 PDs). Crisis occurred significantly earlier (P < 0.05) and the aging process was accelerated in cell lines from SAMP11, compared with lines from SAMR1. This evidence tends to support various observations made in the accelerated senescence-prone strains of SAMP, in vivo.