The effect of age on the induction of tyrosine aminotransferase and tryptophan oxygenase genes by physiological stress

Hepatic tyrosine aminotransferase and glucocorticoid abuse in meat cattle

Besides being extensively applied as therapeutical remedies, glucocorticoids (GCs) - most notably dexamethasone or prednisolone - are also illegally used in livestock for growth-promoting purposes. This study was designed to assess the suitability of liver tyrosine aminotransferase (TAT), a gluconeogenic enzyme known to be induced by GCs, to act as a reliable candidate biomarker to screen for GC abuse in cattle. Enzyme activity was measured spectrophotometrically in liver cytosols or in cell extracts, and TAT gene expression was determined by real-time PCR. Compared with untreated veal calves, a notable scatter (20-fold) and much higher median values (3-fold) characterized TAT specific activity in liver samples from commercially farmed veal calves. A time-related increase in both enzyme activity and gene expression was detected in rat hepatoma cell lines treated with dexamethasone concentrations (10(-8) or 10(-9) m) in the range of those recorded in noncompliant samples from EU official controls. In experimental studies in which finishing bulls were administered GCs at growth-promoting dosages, however, no such changes were recorded in dexamethasone-treated animals; a statistically significant rise in liver TAT activity (+95%) only occurred in prednisolone-treated bulls. Although further research is needed to characterize the GC-mediated response in cattle liver, TAT does not appear to be a specific and sensitive biomarker of GC abuse in the bovine species.

Extension of the life-span of human endothelial cells by an interleukin-1 alpha antisense oligomer

The proliferative potential of human diploid endothelial cells is finite, and cellular senescence in vitro is accompanied by the failure of the endothelial cell to respond to exogenous growth factors. Senescent human endothelial cells were shown to contain high amounts of the transcript for the cytokine interleukin-1 alpha (IL-1 alpha), a potent inhibitor of endothelial cell proliferation in vitro. In contrast, transformed human endothelial cells did not contain detectable IL-1 alpha messenger RNA. Treatment of human endothelial cell populations with an antisense oligodeoxynucleotide to the human IL-1 alpha transcript prevented cell senescence and extended the proliferative life-span of the cells in vitro. Removal of the IL-1 alpha antisense oligomer resulted in the generation of the senescent phenotype and loss of proliferative potential. These data suggest that human endothelial cell senescence in vitro is a dynamic process regulated by the potential intracellular activity of IL-1 alpha.

mRNA levels and methylation patterns of the tyrosine aminotransferase gene in aging inbred rats

We have examined the mRNA levels and methylation patterns of the liver-specific tyrosine aminotransferase (TAT) gene in inbred female rats aged 6, 24 and 36 months. Northern hybridization analysis of total RNA showed a 65% decrease in the steady state transcript level of TAT in the liver of 24- and 36-month old rats as compared to 6-month old animals. The TAT gene as studied by Southern hybridization analysis using the isoschizomers Hpa II and Msp I was found to be hypomethylated in the liver as compared to spleen and brain at six CpG sites within the gene. Methylation at these sites remained unchanged during aging.

Messenger RNA levels and methylation patterns of GAPDH and beta-actin genes in rat liver, spleen and brain in relation to aging

Messenger RNA levels and methylation patterns of the glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) and beta-actin genes were studied in spleen, liver and brain of 6-, 24- and 36-month old female inbred rats. In the spleen, the mRNA levels of both housekeeping genes significantly increased between 24 and 36 months. No age-related alterations in the expression of GAPDH or beta-actin mRNA were observed in brain or liver. A considerable intertissue and interindividual variation was observed in the mRNA levels of these genes in all age-groups as compared to the level of 28 S rRNA, which was used as an internal control. In this respect the interindividual variation in the level of GAPDH mRNA paralleled the variation observed in the beta-actin mRNA level in the three tissues studied. The methylation pattern of beta-actin was found to be tissue-specific in contrast to that of GAPDH, which was identical in all three tissues. No significant age-related alterations were observed in the GAPDH methylation pattern, whereas beta-actin appeared to become slightly demethylated with age in the spleen at the CpG site for which tissue-specificity was observed.

T-kininogen gene expression is induced during aging

We have constructed a cDNA library from senescent (24-month-old) rat liver mRNA and, by differential screening, have selected clones corresponding to mRNA species with increased abundance in aging rats. Direct sequencing of the inserts indicated that most of the clones (9 of 10) contained sequences coding for T-kininogen, also called major acute-phase protein, cysteine protease inhibitor, or thiostatin. Nuclear elongation experiments showed that the increase in mRNA concentration was controlled at the transcriptional level. RNase mapping and S1 analysis indicated that the age-dependent induction operated preferentially at one of the three transcriptional start sites of the gene(s). The acute-phase reaction (inflammation) is known to also induce these genes at the level of transcription; however, two of the three start sites are induced by inflammation. Transcription from one of these sites was induced by both phenomena, aging and inflammation.

T-kininogen gene expression is induced during aging

We have constructed a cDNA library from senescent (24-month-old) rat liver mRNA and, by differential screening, have selected clones corresponding to mRNA species with increased abundance in aging rats. Direct sequencing of the inserts indicated that most of the clones (9 of 10) contained sequences coding for T-kininogen, also called major acute-phase protein, cysteine protease inhibitor, or thiostatin. Nuclear elongation experiments showed that the increase in mRNA concentration was controlled at the transcriptional level. RNase mapping and S1 analysis indicated that the age-dependent induction operated preferentially at one of the three transcriptional start sites of the gene(s). The acute-phase reaction (inflammation) is known to also induce these genes at the level of transcription; however, two of the three start sites are induced by inflammation. Transcription from one of these sites was induced by both phenomena, aging and inflammation.

Variation in the relative abundance of gamma-crystallin gene transcripts during development and ageing

The transcripts of gamma-crystallin mRNA were examined during adulthood. The mRNA transcripts were detected by Northern blot technique. Although the total RNA per lens measured remains constant during adulthood, the mRNA transcript size was observed to decline with ageing, specifically for the gamma-crystallin and not for alpha- and beta-crystallins. We could show that the relative amount of mRNA transcripts detected with the four probes decreased with ageing, with gamma 1 and gamma 2 transcripts being found at a higher level than the gamma 3 and gamma 4 transcripts.