Isolated uterine nuclei and cytosol receptors of aged rats exhibit impaired estrogenic stimulation of RNA polymerase II.

Abstract

An in vitro cell-free system of uterine nuclei and cytosol receptors has been used to analyze the effects of aging on estrogen stimulation of RNA polymerase II activity. By using fixed concentrations of nuclei and cytoplasmic receptor-estrogen complexes (R-E2), it was found that mature nuclei are 3 times more efficient (155% vs. 57%) than old ones for stimulation of polymerase activity by mature R-E2. Meanwhile, mature R-E2 are 5 times more efficient (155% vs. 31 %) than old ones in supporting such stimulation in mature nuclei. Stimulation by old cytosol R-E2 is so poor that it is essentially unaffected by nuclear age (31% with both mature and old nuclei). Finally, equimolar mixtures of mature and old cytosol R-E2 stimulate polymerase II activity in mature nuclei by 77%, a value intermediate between mature and old cytosols used separately. These results indicate that both nuclei and cytosol from old uteri are deficient in their ability to support estrogenic stimulation of RNA polymerase II.The aged rodent uterus exhibits an impaired ability to respond to estrogenic stimulation (refs. 1-3; unpublished data). Examples include reduced or delayed induction of phosphofructokinase (1), phosphohexose isomerase (1), and RNA polymerase 11 (2), as well as decreases in RNA synthesis (3), decidualization response (4), and weight maintainance (4). There is generally good agreement that this impaired responsiveness is at least partially due to loss of estrogen receptors (4-8, *) or reduced receptor translocation into nuclei in vivo (9, 10) during senescence.Although a number of other tissues exhibit similar loss of estrogen receptors and/or responsiveness during aging (11,12), several systems show no receptor loss despite altered hormonal sensitivity (5,(13)(14)(15) (15)(16)(17)(18). It has been shown previously that estrogenic stimulation of uterine RNA polymerase II (2) and total RNA synthesis (3) is reduced during aging in vivo. However, these reductions may simply be the consequence of age-related receptor loss (4-10, *).To determine whether estrogenic stimulation of RNA polymerase II is altered independent of the receptor, it became necessary to establish a cell-free system consisting of isolated uterine nuclei and cytoplasmic receptors. Such a system could allow precise adjustment of nuclear and receptor concentrations as well as heterologous mixing of these components from both mature and old uteri. Some previous reports of analogous cell-free systems have appeared, but these have been restricted to immature animals (19,20).Therefore, the present study has established and utilized a cell-free system from adult animals and examined the effects of aging on the ability of isolated uterine nuclei and cytosol, respectively, to allow estrogenic stimulation of RNA polymerase II. Animals. Mature (6-8 mo) and old (24 mo) female Wistar rats were obtained from the Gerontology Research Center Animal Colony. This colony is fully accredited by the American Association for Accreditation of Laboratory Animal Care. Animals wer...

Characteristics of uterine aging

“…Other studies of ovariectomized Wistar rats have demonstrated that estrogen stimulation of uterine RNA polymerase I1 is reduced in old rats (24 month vs. 6-8 month) and that this effect does not depend on receptor number (Haji et al, 1984). The decline in polymerase I1 stimulation appears to result from a 50% reduction in the number of nuclear binding sites for the estrogen-receptor (ER) complex as the affinity of these sites for the ER complex is not affected by aging (Chuknyiska and Roth, 1985).…”

Altered Hormonal Responsiveness of Proliferation and Apoptosis During Myometrial Maturation and the Development of Uterine Leiomyomas in the Rat1

“…The decreased rates of proliferation and apoptosis observed in myometrium and stroma of 6-to 9-mo-old animals in our study suggests that responsiveness to changes in ovarian hormone levels is dampened in these tissues with increasing age. Data suggest that the ability of E 2 to stimulate DNA synthesis in myometrium and stroma may be impaired in older animals because of changes in both receptor number and function [28,29].…”

Gene Expression and Protein Degradation

“…Semsei et a1 (343) Zs.-Nagy and Semsei (443) In vivo -50 Meerson et al (240) Nuclei -37 Liang et al (201) Haji et al (131) Nuclei -25 to -50 In vivo Increase in most tissues Kanungo et al (166) In vivo - 70 Tonna and Singh (396) Fibroblasts - 50 Chen et al (55) Again, one must be concerned with the accuracy in measuring RNA synthesis in the in vivo studies because the specific activities of the precursor pools were not measured. Figure 9.2 shows the effect of age on the synthesis of RNA by cultured fibroblasts isolated from the skin of human subjects over a wide spectrum of ages.…”