Covalent modifications of chromosomal proteins during aging

Cell-cycle and Age-Related Modulations in Mouse Chromosome Stiffness

The intricate structure of chromosomes is complex, and many aspects of chromosome configuration/organization remain to be fully understood. Measuring chromosome stiffness can provide valuable insights into their structure. However, the nature of chromosome stiffness, whether static or dynamic, remains elusive. In this study, we analyzed chromosome stiffness in MI and MII oocytes. We revealed that MI oocytes had a ten-fold increase in stiffness compared to mitotic chromosomes, whereas chromosome stiffness in MII oocytes was relatively low chromosome. We then investigated the contribution of meiosis-specific cohesin complexes to chromosome stiffness in MI and MII oocytes. Surprisingly, the Young's modulus of chromosomes from the three meiosis-specific cohesin mutants did not exhibit significant differences compared to the wild type, indicating that these proteins may not play a substantial role in determining chromosome stiffness. Additionally, our findings revealed an age-related increase in chromosome stiffness in MI oocytes. Age correlates with elevated DNA damage levels, so we investigated the impact of etoposide-induced DNA damage on chromosome stiffness, discovering a reduction in stiffness in response to such damage in MI oocytes. Overall, our study underscores the dynamic nature of chromosome stiffness, subject to changes influenced by the cell cycle and age.

Age-related patterns of lectin-binding nuclear glycoproteins of hamster liver

We studied the age-related patterns of lectin-binding liver nuclear glycoproteins from hamsters between 5 and 35 weeks of age. The examinations of the carbohydrate structures of liver nuclear glycoproteins in relation to the age of hamsters were carried out after electrophoresis and blotting by a very sensitive immunological detection system with highly specific digoxigenin-labelled lectins. The results reported in the present study do not show any significant changes in the patterns of nuclear glycoproteins with regards to the age of hamsters except the decrease in affinity of wheat germ agglutinin (WGA) to 63 kDa glycoprotein bearing single O-linked N-acetylglucosamine residues.

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.

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 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.

Histone acetylation: a step in gene activation

Cellular ageing appears to consist mainly in a loss of adaptability and a progressive decrease in the capacity of the cell to maintain homeostasis. Such age related phenomenon can be the result of stochastic or of programmed events, and may occur through changes in the base pairs or coding of the DNA, through increasing levels of error in transcription and finally through alterations at the translation step of proteins synthesis. The purpose of this chapter is to present histone acetylation as a key event in the control of chromatin structure and transcription.

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 changes of chromatin. A review

The age-related studies of chromatin and DNA has attracted significant interest in recent years. However, individual works describe only some and a few of the many changes of chromatin. It is often difficult to decide whether these changes have secondary or primary nature. The overview of these studies makes it possible to realize how many very complex and interdependent changes occur in chromatin during ageing. Chromatin is the most complex among self-reproducible parts of the cell. A very sophisticated structure of chromatin makes possible the differential transcription of a genetic programme which supports the accurate specialized functions of each cell in interphase and also provides a mechanism for perfect reproduction of this complex machinery of genetic information during cell division. It is known that chromatin proteins, more than chromatin DNA show tissue specificity and developmental changes. There are many theories of cellular ageing which select some special types of DNA, RNA or protein changes and to promote them as the main or primary causes of cellular senescence. However, if these changes are considered within the more comprehensive picture of functional structure of chromatin the results show the interdependence of individual alterations and their proper place in the complex, multichannel, species and tissue-specific character of actual ageing. An attempt to summarize the basic facts and theories about age changes of the two main parts of chromatin structure, proteins and DNA is being made in this review. At the same time the author tried to develop a concept of non-random distribution of the age changes in chromatin and a possible higher rate of accumulation of different alteration and lesions in the transcribed and functionally active parts of chromatin.

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.