Nucleosomal organization of the rat liver satellite DNA-containing chromatin during aging

Nucleosomal organization of the satellite DNA-containing chromatin of the liver of young (18 +/- 2 weeks) and old (100 +/- 5 weeks) rats was examined by nucleases and satellite I DNA probe. The satellite DNA-containing chromatin exhibits lower accessibility to endogenous endonucleases in old rats. The nucleosomal repeat length of this chromatin as investigated from digestion with endogenous endonucleases and MNase differs remarkably from bulk chromatin, though it does not alter with age. However, age-dependent loss of satellite DNA is apparent from hybridization results. Furthermore, DNase I analysis of the satellite DNA-containing chromatin at nucleosomal level reveals a relatively loose organization in young rats than old ones. It also shows an altered 10 bp periodicity as compared to bulk chromatin in both ages. These findings establish organizational differences between rat liver bulk and satellite DNA-containing chromatin. They further show that repeat length and altered 10 bp periodicity are similar in young and old, but accessibility to nucleases declines with age.

Expression of 112-kDa estrogen receptor in mouse brain cortex and its autoregulation with age

The mouse brain cortex expresses ER whose size is larger than uterus and level changes with age and hormonal treatment. Western blot analysis shows the presence of 66 kDa ER in uterus but 112 and 116 kDa ER in the brain. Whereas 116 kDa ER is phosphorylated and predominantly present in nuclei, 112 kDa ER is unphosphorylated and present in both cytosol as well as nuclei. Similar to uterus, the level of ER decreases drastically in the brain cortex of old mice. Hormonal regulation of ER shows age-specific pattern. Ovariectomy reduces the level of ER in adult but increases it significantly in old. While testosterone does not alter the level of ER in either age, estradiol decreases it considerably in old but shows no detectable difference in adult. Our results provide evidence for the expression of a novel form of ER in mouse brain cortex and its regulation by sex steroid hormones in age-specific manner.

Age-related analysis of EcoRI generated satellite DNA-containing chromatin of rat liver

EcoRI digestion of nuclei and their subsequent lysis with EDTA solubilizes 45% and 36% of chromatin DNA from the liver of young (18 +/- 2 weeks) and old (100 +/- 5 weeks) rats, respectively. After hybridization with 185 bp rat satellite I DNA, these soluble fractions are found to be enriched in specific DNA sequences such as satellite DNA. Besides regular repeat pattern, a major portion of the satellite chromatin forms higher order organization. Digestion kinetics confirms condensation of satellite DNA-containing chromatin similar to that of bulk chromatin in old age. Furthermore, densitometric scanning of the slot-blot of soluble chromatin fractions reveals loss of satellite DNA in the old. However, an increase in the linker histone H1 and its subfraction H1zero in the satellite DNA-enriched fraction of chromatin from old rats suggests greater compaction. These results provide the first evidence that the satellite DNA-containing chromatin differs in the liver of young and old rats.

Androgen treatment protects mouse liver chromatin from cleavage by endogenous nucleases during aging. Androgen and nuclease activity

We have examined the endogenous nuclease activity of the liver of intact, castrated and testosterone-treated mice of different ages. Both Mg(2+)- and Ca(2+)-dependent endogenous nuclease activities decline in old age. Withdrawal of the hormone increases nuclease activity in the immature and young. However, testosterone administration prevents the digestion of nuclei to different extents in all ages. These findings suggest a possible protective role of testosterone in the cleavage of liver chromatin by endogenous nucleases during the aging of mice.

Gene expression and aging

Considerable amount of data has accumulated during the past few years showing several changes in gene expression as a function of age. However, the basic mechanism of aging still remains poorly understood. In this review, we have mainly analysed the data pertaining to the hypothesis that aging is associated with genetic instability and have attempted further to highlight the gaps that need to be bridged in order to have a clear picture of the aging phenomenon. Extensive investigations employing new and novel approaches are needed in future to elucidate the intricately interwoven patterns of molecular control that underlie the various aspects of gene expression during aging.

Phenylmethylsulfonyl fluoride stimulates proteolysis of nuclear proteins from chick liver

The degradation of H1 histone and high mobility group (HMG) nonhistone proteins was stimulated when the homogenate from chick liver was incubated in the presence of phenylmethylsulfonyl fluoride (PMSF). Two proteinase inhibitors, elastatinal and chymostatin, significantly inhibited the PMSF-stimulated degradation of H1 histone and HMG proteins. On the contrary, other proteinase inhibitors like leupeptin, pepstatin, trypsin inhibitor, antipain, o-phenanthroline and EDTA had no effect on the degradation of the nuclear proteins. These results warn the researcher to be cautious while using PMSF for preparation of nuclear proteins such as H1 histone and HMG proteins.

Estrogen-induced synthesis of uterine proteins declines during aging

The synthesis of total cellular as well as acid-soluble nuclear proteins and estrogen receptor is high in the uteri of young (22 weeks) and decreases to half in old (104 weeks) rats. Administration of estrogen induces the synthesis of these proteins significantly in young but shows no remarkable effect in old rats. Interestingly, a specific cytosolic protein of 45 kDa is stimulated about two-fold after estrogen injection in young but not in old rats. These findings further establish the reduced responsiveness of uterus to estrogen in old age.

Methylation of DNA and its modulation by estrogen in the uterus of aging rats

The effect of estrogen on methylation of DNA from the uteri of young (20 weeks) and old (96 weeks) female Wistar rats has been examined by isoschizomeric restriction enzymes and HPLC analysis. In vitro methylation of DNA is significantly higher in the uteri of young rats as compared to old ones. This is reduced by estrogen to greater extent in young than in old age. Furthermore, the digestion of DNA with EcoRI+Msp I shows a distinct 1.2 kb band only in young control. Such band is absent in old control and estrogen-treated sets of both age groups. The HPLC data further reveal that the level of 5-methyl cytosine is high in young and decreases by nearly 18% in old. Estrogen lowers the level of 5-methyl cytosine by 8% in young but shows no effect in the old. Such age-dependent changes in the methylation of DNA brought by estrogen in the rat uterus attribute to alterations in gene expression during aging.

Differential methylation of HMG proteins by dexamethasone in the liver of aging rats

In vitro methylation of HMG proteins was studied in young and old rats by incubating liver slices with (methyl-14C)methionine. The level of methylation of all the four HMG proteins was relatively higher in young, as compared to old rats. Dexamethasone stimulated the methylation of HMG 2 to 12-fold, and inhibited that of other HMGs in young rats. On the other hand, it stimulated all major HMG proteins except HMG 2, which remains unchanged in old age. Such differential methylation of HMG proteins induced by dexamethasone affects the structure and function of chromatin during aging.

Effect of age on physico-chemical properties of the uterine nuclear estrogen receptors of albino rats

Estrogen receptors (ER) were extracted with high ionic strength buffer from the nuclei of uteri of young (21 weeks) and old (89 weeks) rats. Following the analysis of these receptors on a sucrose gradient and a Sephadex column, two peaks representing the two forms of receptors were obtained. The minor peak sedimented at 6.8 S with Stokes radius (RS) = 7.2 nm, molecular weight (Mr) = 204 K and frictional ratio (f/f0) = 1.71. On the other hand, the major peak sedimented at 4.1 S with RS = 3.3 nm, Mr = 57 K and f/f0 = 1.18. These properties of nuclear ER were similar in both ages. Also, the half life of ER complexes from both ages at 25 degrees C and 37 degrees C were 135 min and 30 min, respectively. However, these complexes were retained for longer periods in the nuclei of young than old rats. Furthermore, the dissociation constant of the binding of nuclear receptors to estrogen remained constant, but the number of binding sites decreased from 1.56 in young to 1.05 pmol/mg DNA in the old. In young rats, about 61% of nuclear receptors bound to DNA-cellulose. Out of this 2/5 was eluted with 0.15 M and the remaining 3/5 with 0.5 M KCl. On contrary, only 37% of total receptors bound to DNA-cellulose in the old. Out of this 3/5 was eluted with 0.15 M and the remaining 2/5 with 0.5 M KCl. These data suggested that despite the similarity in different physicochemical properties, the number of estrogen binding sites and the retention time of ER complexes in nuclei and the ability of these complexes to bind to DNA decrease in the uterus of old age.

Analysis of age-associated alteration in the synthesis of HMG nonhistone proteins of the rat liver

HMG proteins were extracted with 5% PCA or 0.35 M NaCl from whole tissue, nuclei or chromatin of the liver of young (19 weeks) and old (118 weeks) male rats. They were resolved on acetic acid-urea polyacrylamide gel. The electrophoretic patterns of the major HMG proteins 1, 2, 14 and 17 of both ages are similar. The in vitro synthesis of HMG 1 and 2 decreases, but that of HMG 14 and 17 increases considerably in the liver of old rats. The synthesis of different HMG proteins is modulated differentially by spermine, butyrate, dexamethasone and 3-aminobenzamide in the liver of young and old rats. These findings suggest that HMG proteins contribute to alterations in the organization of chromatin and expression of genes during aging.

Effect of post-synthetic modifications of proteins on the binding of estrogen-receptor complex to uterine nuclei of aging rats

The binding of estrogen-receptor (ER) complex to nuclei following post-synthetic modifications of proteins was examined in the uteri of young (18 weeks) and old (96 weeks) rats. Acetylation decreases the binding of ER complex to nuclei but methylation shows no effect on the extent of binding in both ages. On the other hand, phosphorylation enhances the binding of ER complex by two-fold in nuclei from young rats but reduces this to half in nuclei from old rats. The pattern of binding in salt-resistant nuclear fractions is similar to that in total nuclei except in methylation where old rats show about 20% higher binding as compared to the respective control. These findings suggest that post-synthetic modifications of proteins modulate the binding of ER complex to uterine nuclei in an age-specific manner.

Effects of spermine and sodium butyrate on the in vitro phosphorylation of HMG non-histone proteins of the liver of young and old rats

The in vitro phosphorylation of high mobility group (HMG) proteins and its modulation by spermine and sodium butyrate were studied in the liver of young (15 week) and old (138 week) male rats. Except HMG 1 which remained unchanged, the phosphorylation of other proteins (HMG 2, 14 and 17) decreased drastically in old age. Spermine stimulated the phosphorylation of HMG 1 and 17 in young but HMG 1, 2 and 14 in old rats. The incorporation of (32)P into total HMG proteins was enhanced by butyrate in the liver of both ages. However, the degree of stimulation was higher in young rats. Particularly, the HMG 1 and 17 of young and HMG 2 and 17 of old rats showed increased phosphorylation. Furthermore, butyrate also inhibited the phosphorylation of HMG 2 in young and HMG 1 and 14 in old rats. Such alteration in the phosphorylation of major HMG proteins modulates their interaction with DNA and other components of chromatin. This may account for changes in the higher order organization of chromatin and expression of genes during aging.

ADP-ribosylation of HMG proteins and its modulation by different effectors in the liver of aging rats

The in vitro ADP-ribosylation of high mobility group (HMG) non-histone proteins and its modulation by spermine, butyrate, dexamethasone and 3-aminobenzamide were studied in the liver of young (14 weeks) and old (113 weeks) male rats. ADP-ribosylation of HMG 1 was similar in both ages, whereas that of HMG 2 and 14 decreased but HMG 17 increased in the old. HMG 1 was ADP-ribosylated to a greater extent in young but to a lower level in the old by different effectors except spermine which showed no influence in old age. ADP-ribosylation of HMG 2 was stimulated by spermine, butyrate and dexamethasone in old but only by spermine in young rats. Other effectors decreased the ADP-ribosylation of HMG 2 in young. The ADP-ribosylation of HMG 14 was stimulated by spermine in the old but that of HMG 17 was reduced by butyrate in young and by spermine in the old. Dexamethasone decreased the ADP-ribosylation of both HMG 14 and 17 in young, whereas this showed no change in old age. Aminobenzamide inhibited ADP-ribosylation of only HMG 2 in young but all HMGs except HMG 2 in the old. Such alteration in the ADP-ribosylation of HMG proteins may affect various cellular and nuclear functions of rat liver during aging.

Age-specific methylation of high-mobility-group proteins of the rat liver and its modulation by spermine and sodium butyrate

Liver slices from young (20 weeks) and old (117 weeks) rats were incubated with [methyl-14C]methionine in the absence or presence of spermine or sodium butyrate. The high-mobility-group (HMG) non-histone proteins were extracted from the liver with perchloric acid and separated by acid-urea polyacrylamide slab gel electrophoresis. Methylation of HMG proteins decreased drastically in old rats. Whereas spermine inhibited the methylation of total HMG proteins in young rats, it had no effect in old age. On the contrary, sodium butyrate did not change the incorporation of methyl groups into total HMG proteins of young rats, but inhibited that of old rats. Particularly, the incorporation of [14C]methyl groups into HMG 2 was enhanced but into other HMGs it was reduced by both effectors in young and old age. Such discrepancies in the methylation of HMG proteins and their differential modulation by spermine and butyrate might affect the higher-order organization of chromatin and consequently destabilize the expression of genes during aging.

In vitro acetylation of the liver HMG non-histone proteins and its modulation by spermine and dexamethasone during aging of rats

The in vitro acetylation of HMG proteins was studied using liver slices of young (18-week) and old (138-week) male rats. Acetylation of total HMG proteins is lower in old age. The incorporation of (14C) acetate into individual HMG proteins varies remarkably with advancing age. Whereas acetylation of high mol. wt. proteins (HMG 1 and 2) is higher, that of low mol. wt. proteins (HMG 14 and 17) is lower in the liver of young rats as compared to the old ones. Spermine stimulates the acetylation of HMG 1 and 14 in young and HMG 1, 2 and 14 in old age. It inhibits the acetylation of HMG 17 in both ages. Dexamethasone decreases the level of incorporation of (14C) into HMG 1 and 17 in young and HMG 14 and 17 in old rats. On the other hand, it stimulates the acetylation of HMG 14 by two-fold in young and that of HMG 1 and 2 by more than three-fold in old rats. Such alteration in the acetylation of HMG proteins may account for age-related changes in the structure and function of chromatin.

Molecular mechanism of steroid hormone action during aging. A review

The application of immunochemistry coupled with genetic engineering techniques has helped greatly in the understanding of the molecular mechanism of steroid hormone action. Particularly, the recent observations on nuclear localization of steroid receptor proteins and the interaction of the steroid-receptor complex with the genome have provided much insight into the whole pathway of steroid hormone action. Despite the large amount of data accumulated over the years on the mechanism of steroid action in general, relatively little is known about the changes occurring in the action of steroid hormones during aging. However, there is some evidence of a decreased responsiveness of target tissues to steroid hormones during senescence. In the light of recent progress in steroid research, an attempt has been made in this article to discuss the alterations that occur at different steps of steroid action as a function of age.

Age-dependent effects of sodium butyrate and hydrocortisone on acetylation of high mobility group proteins of rat liver

The in vitro acetylation of high mobility group (HMG) proteins and its modulation by sodium butyrate and hydrocortisone have been studied using liver slices of young (13-) and old (114-week-old) rats. Acetylation of total HMG proteins was significantly higher in young than old rats. HMG 1, in particular, showed greater acetylation than others. Whereas acetylation of HMG 1 and 2 decreased drastically, that of HMG 14 and 17 increased in old age. In young rats, sodium butyrate and hydrocortisone stimulated acetylation of HMG 14 and 17, and decreased that of HMG 2. Butyrate had no effect on HMG 1, but hydrocortisone decreased it. In old rats, butyrate and hydrocortisone decreased acetylation of all HMGs, except HMG 17, which was stimulated to a slight extent by butyrate.

Dexamethasone-induced phosphorylation of high mobility group nonhistone proteins of aging rats

Phosphorylation of high mobility group (HMG) proteins and its modulation by dexamethasone were examined in vitro by incubating liver slices of young (15-) and old (138-week) male rats with (32P) orthophosphate. HMG proteins were extracted and analyzed by acid-urea polyacrylamide gel electrophoresis. Phosphorylation of HMG proteins, particularly of HMG2, 14 and 17 decreases drastically in old rats. Dexamethasone stimulates the phosphorylation of total HMG proteins in both ages. Individual HMG proteins vary in the extent of 32P incorporation. Such differential phosphorylation of HMG proteins and its modulation by dexamethasone may affect chromatin organization and gene expression during aging.

Age-related changes in the structure and function of chromatin: a review

Due to rapid advancement in biochemical and biophysical techniques during the last decade, extensive studies have been undertaken to understand the structure and function of chromatin. Several interesting results have been reported regarding the changes in basic organization and function of chromatin during the life time of a eukaryotic cell. The data accumulated so far have been obtained with different organs and organisms and widely differing methods, and the conclusions drawn from them are sometimes contradictory. In this paper, therefore, the available data on the age-associated alterations in the composition, structure and function of chromatin have been discussed, and an attempt has been made to correlate the structural changes in chromatin with alteration in gene expression during aging.

Covalent modifications of chromosomal proteins during aging

Covalent modifications of proteins introduce negative or positive charges into the molecules and thereby cause alterations in the ionic interactions of protein-protein or DNA-protein complexes. Whereas modifications of histones largely affect the organization of chromatin, those of non-histone proteins are believed to be involved in the expression of genes. These modifications during aging have been reviewed here. The available data suggest that the extent of covalent modifications of histones and non-histone chromosomal (NHC) proteins change during aging and such modifications may have an important role in the differential expression of genes at different phases of life span of an organism.