Ageing and the mystery at Arles.
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Aging↗
Biomedical subjects
Toren Finkel
Publications and source records attributed to Toren Finkel.
Pharmacology: uncoupling the agony from ecstasy.
The recreational use of amphetamine-type stimulants can produce a marked and sometimes lethal increase in body temperature. Here we show that mice deficient in a mitochondrial protein known as UCP-3 (for 'uncoupling protein-3') have a diminished thermogenic response to the drug MDMA (3,4-methylenedioxymethamphetamine, nicknamed 'ecstasy') and so are protected against this dangerously toxic effect. Our findings indicate that UCP-3 is important in MDMA-induced hyperthermia and point to a new therapeutic direction for solving an increasing public-health problem.
Animals↗
Ageing: a toast to long life.
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Acetylation↗
Circulating endothelial progenitor cells, vascular function, and cardiovascular risk.
BACKGROUND: Cardiovascular risk factors contribute to atherogenesis by inducing endothelial-cell injury and dysfunction. We hypothesized that endothelial progenitor cells derived from bone marrow have a role in ongoing endothelial repair and that impaired mobilization or depletion of these cells contributes to endothelial dysfunction and cardiovascular disease progression. METHODS: We measured the number of colony-forming units of endothelial progenitor cells in peripheral-blood samples from 45 men (mean [+/-SE] age, 50+/-2 years). The subjects had various degrees of cardiovascular risk but no history of cardiovascular disease. Endothelium-dependent and endothelium-independent function was assessed by high-resolution ultrasonography of the brachial artery. RESULTS: We observed a strong correlation between the number of circulating endothelial progenitor cells and the subjects' combined Framingham risk factor score (r=-0.47, P=0.001). Measurement of flow-mediated brachial-artery reactivity also revealed a significant relation between endothelial function and the number of progenitor cells (r=0.59, P<0.001). Indeed, the levels of circulating endothelial progenitor cells were a better predictor of vascular reactivity than was the presence or absence of conventional risk factors. In addition, endothelial progenitor cells from subjects at high risk for cardiovascular events had higher rates of in vitro senescence than cells from subjects at low risk. CONCLUSIONS: In healthy men, levels of endothelial progenitor cells may be a surrogate biologic marker for vascular function and cumulative cardiovascular risk. These findings suggest that endothelial injury in the absence of sufficient circulating progenitor cells may affect the progression of cardiovascular disease.
Adult↗
Oxidant signals and oxidative stress.
Although oxidants clearly possess the capacity to behave in a random and destructive fashion, growing evidence suggests that in many instances the production of reactive oxygen species is tightly regulated and their downstream targets exquisitely specific. This past year, several notable advances have been made in defining the specific redox-dependent targets of intracellular oxidants, as well as the myriad pathways that appear to employ oxidants as effector molecules. These new studies have significantly altered our understanding of how reactive oxygen species participate in diverse processes from tumourigenesis to ageing.
Animals↗
Neutrophils with a license to kill: permeabilized, not stirred.
The neutrophil responds to invading microorganisms in part by assembling the NADPH oxidase complex and producing superoxide radicals. Relatively little is known about the intracellular assembly or activation of the oxidase, but Brown et al. in the January issue of Molecular Cell provide a useful strategy involving permeabilized neutrophils to tackle this question.
Cell Death↗
Identification of a specific molecular repressor of the peroxisome proliferator-activated receptor gamma Coactivator-1 alpha (PGC-1alpha).
The nuclear co-activator PGC-1alpha is a pivotal regulator of numerous pathways controlling both metabolism and overall energy homeostasis. Inappropriate increases in PGC-1alpha activity have been linked to a number of pathological conditions including heart failure and diabetes mellitus. Previous studies (Puigserver, P., Adelmant, G., Wu, Z., Fan, M., Xu, J., O'Malley, B., and Spiegelman, B. M. (1999) Science 286, 1368-1371) have demonstrated an inhibitory domain within PGC-1alpha that limits transcriptional activity. Using this inhibitory domain in a yeast two-hybrid screen, we demonstrate that PGC-1alpha directly associates with the orphan nuclear receptor estrogen-related receptor-alpha (ERR-alpha). The binding of ERR-alpha to PGC-1alpha requires the C-terminal AF2 domain of ERR-alpha. PGC-1alpha and ERR-alpha have a similar pattern of expression in human tissues, with both being present predominantly in organs with high metabolic needs such as skeletal muscle and kidney. Similarly, we show that in mice physiological stimuli such as fasting coordinately induces PGC-1alpha and ERR-alpha transcription. We also demonstrate that under normal conditions PGC-1alpha is located within discrete nuclear speckles, whereas the expression of ERR-alpha results in PGC-1alpha redistributing uniformly throughout the nucleoplasm. Finally, we show that the expression of ERR-alpha can dramatically and specifically repress PGC-1alpha transcriptional activity. These results suggest a novel mechanism of transcriptional control wherein ERR-alpha can function as a specific molecular repressor of PGC-1alpha activity. In addition, our results suggest that other co-activators might also have specific repressors, thereby identifying another layer of combinatorial complexity in transcriptional regulation.
Binding Sites↗
Regulation of the Werner helicase through a direct interaction with a subunit of protein kinase A.
Werner syndrome is a hereditary disease characterized by cancer predisposition, genetic instability, and the premature appearance of features associated with normal aging. At the molecular level this syndrome has been related to mutations in the Werner helicase, a member of the RecQ family of DNA helicases which are required to maintain genomic stability in cells. Here we show by a yeast two-hybrid screen that the Werner helicase can directly interact with the regulatory subunit (RIbeta) of cAMP protein kinase A (PKA). We confirm that this interaction occurs in vivo. Interestingly, serum withdrawal causes a redistribution of the Werner helicase within the nucleus of mammalian cells. Raising intracellular cAMP levels or increased expression of the regulatory but not the catalytic subunit of PKA inhibits this nuclear redistribution stimulated by serum deprivation. These results suggest that similar to lower organisms, gene products linked to genomic instability and aging may be directly regulated by growth factor-sensitive, PKA-dependent pathways.
Binding Sites↗
A role for mitochondria as potential regulators of cellular life span.
We demonstrate that by simply raising extracellular pyruvate levels, and hence increasing metabolic supply, human diploid fibroblasts undergo a concentration-dependent induction of cellular senescence. Fibroblasts treated with pyruvate undergo a rapid growth arrest accompanied by elevated levels of the cell-cycle regulatory molecules p53, p21, and p16. These cells also exhibit a rise in mitochondrial oxidant production and a fall in intracellular glutathione levels. Exposure of pyruvate treated cells to the antioxidant and glutathione precursor N-acetylcysteine restores cell growth and reverses the increase in senescence-associated beta-galactosidase activity. Similarly, we demonstrate that by increasing mitochondrial number via retroviral-mediated expression of the mitochondrial biogenesis regulator PGC-1 there is also a reduction in cell growth and the more rapid induction of senescence. These results suggest that mitochondria appear to play a central role in regulating cellular life span.
Acetylcysteine↗
Regulation of cellular oncosis by uncoupling protein 2.
Cell death can proceed through at least two distinct pathways. Apoptosis is an energy-dependent process characterized morphologically by cell shrinkage, whereas oncosis is a form of cell death induced by energy depletion and initially characterized by cell swelling. We demonstrate in HeLa cells but not in normal diploid fibroblasts that modest increases in the expression level of uncoupling protein 2 (UCP-2) leads to a rapid and dramatic fall in mitochondrial membrane potential and to a reduction of mitochondrial NADH and intracellular ATP. In HeLa cells, increased UCP-2 expression leads to a form of cell death that is not inhibited by the anti-apoptotic gene product Bcl-2 and that morphologically resembles cellular oncosis. We further describe the creation of a dominant interfering mutant of UCP-2 whose expression increases resting mitochondrial membrane potential and selectively increases the resistance to cell death following oncotic but not apoptotic stimuli. These results suggest that distinct genetic programs may regulate the cellular response to either apoptotic or oncotic stimuli.
Apoptosis↗
Redox regulation of Cdc25C.
The Cdc25 family of dual specific phosphatases are critical components of cell cycle progression and checkpoint control. Certain stresses such as ultraviolet light stimulate the rapid and selective destruction of Cdc25A protein through a Chk1 protein kinase-dependent pathway. We demonstrate that in contrast to cellular stresses previously examined, hydrogen peroxide exposure affects Cdc25C but not Cdc25A levels. Pharmacological inhibition of Chk1 activity or a mutant of Cdc25C that lacks the Chk1 phosphorylation site still undergoes degradation in response to oxidants. We also demonstrate that in vitro hydrogen peroxide stimulates an intramolecular disulfide bond between the active site cysteine at position 377 and another invariant cysteine at position 330. The in vivo stability of Cdc25C is substantially reduced by the mutation of either of these two cysteine residues. In contrast, a double (C2) mutant of both cysteine 330 and cysteine 377 results in a protein that is more stable than wild type Cdc25C and is resistant to oxidative stress-induced degradation. In addition, the C2 mutant, which is unable to form an intramolecular disulfide bond, has reduced binding to 14-3-3 in vitro and in vivo. These results suggest that oxidative stress may induce cell cycle arrest in part through the degradation of Cdc25C.
Cell Cycle Proteins↗
Redox regulation of forkhead proteins through a p66shc-dependent signaling pathway.
Genetic determinants of longevity include the forkhead-related transcription factor DAF-16 in the worm Caenorhabditis elegans and the p66shc locus in mice. We demonstrate that p66shc regulates intracellular oxidant levels in mammalian cells and that hydrogen peroxide can negatively regulate forkhead activity. In p66shc-/- cells, the activity of the mammalian forkhead homolog FKHRL1 is increased and redox-dependent forkhead inactivation is reduced. In addition, expression of FKHRL1 results in an increase in both hydrogen peroxide scavenging and oxidative stress resistance. These results demonstrate an important functional relation between three distinct elements linked to aging: forkhead proteins, p66shc, and intracellular oxidants.
Acetylcysteine↗
Detection and affinity purification of oxidant-sensitive proteins using biotinylated glutathione ethyl ester.
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Annexin A2↗
Oxidants painting the cysteine chapel: redox regulation of PTPs.
Growth factors and cytokines appear to stimulate the intracellular production of reactive oxygen species (ROS). Evidence suggests that this alteration in the cellular redox state is essential for downstream signaling, but the precise mechanism has remained elusive. A new study now demonstrates that ligand-stimulated intracellular hydrogen peroxide can specifically and reversibly regulate the activity of protein tyrosine phosphatases.
Cysteine↗
Reactive oxygen species as mediators of cellular senescence.
Aging has often been viewed as a random process arising from the accumulation of both genetic and epigenetic changes. Increasingly, the notion that aging is a stochastic process is being supplanted by the concept that maximum lifespan of an organism is tightly regulated. This knowledge has led to a growing overlap between classical signal transduction paradigms and the biology of aging. We review certain specific examples where these seemingly disparate disciplines intersect. In particular, we review the concept that intracellular reactive oxygen species function as signalling molecules and that oxidants play a central role as mediators of cellular senescence.
Animals↗
Intracellular redox regulation by the family of small GTPases.
There is growing experimental evidence that the production of intracellular reactive oxygen species (ROS) represents a tightly regulated process. In particular, numerous observations have suggested a role for the Ras superfamily of small GTPases in redox regulation. This article reviews the evidence that ROS can serve as important downstream effectors for both Ras and Rac proteins. Given the prominent role these proteins play in regulating growth, senescence, and transformation, understanding the role of the small GTPase family in redox regulation may significantly alter our current concepts as to how free radicals contribute to diverse processes from aging to cancer.
Animals↗
Mitochondrial signaling, TOR, and life span.
Growing evidence supports the concept that mitochondrial metabolism and reactive oxygen species (ROS) play a major role in aging and determination of an organism's life span. Cellular signaling pathways regulating mitochondrial activity, and hence the generation of ROS and retrograde signaling events originating in mitochondria, have recently moved into the spotlight in aging research. Involvement of the energy-sensing TOR pathway in both mitochondrial signaling and determination of life span has been shown in several studies. This brief review summarizes the recent progress on how mitochondrial signaling might contribute to the aging process with a particular emphasis on TOR signaling from invertebrates to humans.
Aging↗