Response of the Senescent Heart to Stress: Clinical Therapeutic Strategies and Quest for Mitochondrial Predictors of Biological Age

The involvement of stress granules in aging and aging-associated diseases

Stress granules (SGs) are nonmembrane assemblies formed in cells in response to stress conditions. SGs mainly contain untranslated mRNA and a variety of proteins. RNAs and scaffold proteins with intrinsically disordered regions or RNA-binding domains are essential for the assembly of SGs, and multivalent macromolecular interactions among these components are thought to be the driving forces for SG assembly. The SG assembly process includes regulation through post-translational modification and involvement of the cytoskeletal system. During aging, many intracellular bioprocesses become disrupted by factors such as cellular environmental changes, mitochondrial dysfunction, and decline in the protein quality control system. Such changes could lead to the formation of aberrant SGs, as well as alterations in their maintenance, disassembly, and clearance. These aberrant SGs might in turn promote aging and aging-associated diseases. In this paper, we first review the latest progress on the molecular mechanisms underlying SG assembly and SG functioning under stress conditions. Then, we provide a detailed discussion of the relevance of SGs to aging and aging-associated diseases.

Oxidative Stress Increases the Number of Stress Granules in Senescent Cells and Triggers a Rapid Decrease in p21waf1/cip1 Translation

Very little is known as to how the accumulation of senescent cells during aging may affect our ability to cope with various stresses. Here we show that the assembly of stress granules (SGs) is part of the early events used by senescent cells to respond to certain stresses. Although SGs can form in response to stress during senescence activation, their number significantly increases once the cells are fully senescent. This increase correlates with a rapid decrease in the expression levels of the cyclin kinase inhibitor p21, an important activator of senescence. Throughout stress, p21 mRNA is stabilized and localizes to SGs, but only during late senescence does this localization interferes with its translation. Additionally, we observed that when the stress is relieved, senescent cells produce lower levels of p21 protein, which correlates with a small delay in SG disassembly. Therefore, our data suggest that SG formation and the reduction in p21 protein levels represent two main events by which senescent cells respond to stress.

Selenium status of the Australian population: effect of age, gender and cardiovascular disease

Selenium (Se) is an essential trace element and the clinical consequences of Se deficiency have been well-documented. Se is primarily obtained through the diet and recent studies have suggested that the level of Se in Australian foods is declining. Currently there is limited data on the Se status of the Australian population so the aim of this study was to determine the plasma concentration of Se and glutathione peroxidase (GSH-Px), a well-established biomarker of Se status. Furthermore, the effect of gender, age and presence of cardiovascular disease (CVD) was also examined. Blood plasma samples from healthy subjects (140 samples, mean age = 54 years; range, 20-86 years) and CVD patients (112 samples, mean age = 67 years; range, 40-87 years) were analysed for Se concentration and GSH-Px activity. The results revealed that the healthy Australian cohort had a mean plasma Se level of 100.2 +/- 1.3 microg Se/L and a mean GSH-Px activity of 108.8 +/- 1.7 U/L. Although the mean value for plasma Se reached the level required for optimal GSH-Px activity (i.e. 100 microg Se/L), 47% of the healthy individuals tested fell below this level. Further evaluation revealed that certain age groups were more at risk of a lowered Se status, in particular, the oldest age group of over 81 years (females = 97.6 +/- 6.1 microg Se/L; males = 89.4 +/- 3.8 microg Se/L). The difference in Se status between males and females was not found to be significant. The presence of CVD did not appear to influence Se status, with the exception of the over 81 age group, which showed a trend for a further decline in Se status with disease (plasma Se, 93.5 +/- 3.6 microg Se/L for healthy versus 88.2 +/- 5.3 microg Se/L for CVD; plasma GSH-Px, 98.3 +/- 3.9 U/L for healthy versus 87.0 +/- 6.5 U/L for CVD). These findings emphasise the importance of an adequate dietary intake of Se for the maintenance of a healthy ageing population, especially in terms of cardiovascular health.

Processing, lysis, and elimination of brain lipopigments in rejuvenation therapies

Cerebral lipopigments (LPs)--lipofuscin and ceroid--represent a significant marker in postmitotic normal and pathologic aging, connected with causal and associated neuropathologic damage. Therefore, LP processing, lysis, and elimination may be the main targets in anti-aging and rejuvenation therapies. The regenerative neuroactive factors improve neuron supply with specific nutrients from plasma. They enhance the antioxidative defense, have anti-LP-poietic actions, stimulate brain anabolism, support energetic metabolism, and elevate the reduced lysosomal enzymes. In the second stage, by cytoplasm rehydration, they initiate the breaking up of the neuronal aggregated LP conglomerates, by consecutive disintegration. Then, possibly by the localized exo-endocytosis process between neurons and adjacent glia (especially microglia), intercellular LP transfer can be realized. So, therapeutically activated glia turn into brain garbage collectors and transporters. Therapeutic processing of glial LPs increases in the capillary neighborhood. Highly processed LPs, by glio-endothelial transfer, reach capillary walls before being eliminated. Consequently, neuroactive therapies having these synergistic rejuvenative actions represent new prospects in deceleration of normal and pathological cerebral aging.

Decrease in NADPH-Cytochrome P450 Reductase Activity of the Human Heart, Liver and Lungs in the Presence of Alpha-Lipoic Acid

BACKGROUND

NADPH-cytochrome P450 reductase (CPR) is the electron donor protein for several oxygenase enzymes located in the endoplasmic reticulum. These oxygenases include P450 family enzymes involved in the metabolism of endogenous and exogenous substances. The enzyme is involved in adriamycin (anticancer drug) and paraquat (herbicide) toxicity. CPR is a flavoprotein containing both flavine-adenine dinucleotide and flavine mononucleotide. A structural study showed the presence of several sulfhydryl (SH) groups in the CPR molecule. Some of them play a key role in catalytic activity. As alpha-lipoic acid contains a disulfide bond, it may react with the SH group of CPR. The aim of the study was to evaluate the effect of alpha-lipoic acid on human P450 reductase activity.

METHODS

The activity of the enzyme was determined by measuring the rate of cytochrome c reduction at 550 nm, in vitro, using heart, liver and lung microsomes.

RESULTS

The activity of CPR was decreased in all organs after addition of alpha-lipoic acid to the reaction mixture at concentrations of 0.01, 0.10 and 1.00 mM. The decreases in CPR activity were concentration-dependent and the sequence of relative inhibition was as follows: heart >lung >liver. However, the statistical significance of CPR activity vs. control was observed in the heart in the presence of 1.00 mM alpha-lipoic acid and in the lung at 0.10 and 1.00 mM alpha-lipoic acid.

CONCLUSION

alpha-Lipoic acid decreased NADPH-CPR activity in the lung and heart. The present results are promising for future studies to obtain the most effective antidote for adriamycin and paraquat toxicity.

Where and When Do Somatic mtDNA Mutations Occur?

It is generally assumed that somatic mtDNA mutations are originally created in the cells where these mutations are currently found. Accumulating data indicate, however, that cells with a particular mtDNA mutation tend to "cluster," that is, occur repeatedly within a given sample, but not in the others. Clusters likely are clonal, which implies that mtDNA mutations do not originate in the cells that currently carry them, but rather in those cells' progenitors, such as stem or satellite cells, or even earlier in the development. Importantly, a majority of mtDNA mutations appear to belong to such clusters, and thus mutational events in progenitor cells may be one of the major sources of mtDNA mutations in healthy aging tissue. More research including the analysis of multiple samples per individual is needed to confirm the existence of clustering and to distinguish between the possible clustering mechanisms.