Link: http://www.the-scientist.com/2005/5/9/22/1

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Autophagy & Longevity
How keeping house may keep one young | By Jill U. Adams

During autophagy-literally "self-eating"-cells deliver cytoplasmic constituents, including whole organelles, to the lysosome for degradation. This crucial recycling process kicks in during gross developmental changes and times of nutrient deprivation. New work may place it within cellular aging pathways as well.

Characterized morphologically by Christian de Duve in the 1960s, autophagy was a natural extension of his Nobel Prize-winning work on lysosomes. Veteran researchers in a once obscure field point to the discovery of the molecular machinery a decade ago-autophagy gene products that drive the process-as a boost to their own work. More recently, the linkage of one of these genes with tumorigenesis placed autophagy under a new spotlight and is credited with widening the investigative pool. Now scientists are finding evidence-both circumstantial and causal-that autophagy is a key mechanism in how certain manipulations, namely mutations in insulin signaling and caloric restriction, promote longevity.

Autophagy often gets overlooked as "just housekeeping," says Beth Levine, professor of internal medicine at the University of Texas-Southwestern Medical Center at Dallas. In fact, she says, failures in keeping house likely contribute to diseases such as cancer and neurodegeneration. In addition, autophagy wanes with age for reasons that aren't yet clear, says Levine, and is "mechanistically important" in aging itself.

FROM FEAST TO FAMINE When food is scarce, autophagy gets turned on as a survival mechanism. When food is moderately restricted for a long time, organisms from worms to mammals live longer. Ettore Bergamini, professor of pathology at the University of Pisa, Italy, provides some evidence that increased autophagy may accompany calorie-restricted life extension. In rats subject to caloric restriction, autophagic efficiency is maintained in old age and rats live longer.1

"The problem of aging is free radical production and imperfection of the cell-repair mechanisms," says Bergamini. Perhaps more general contractor than housekeeper, autophagy is a "second-line defense" against the maintenance challenges of cells. "One hundred million free radicals are generated per day in our body," he says. "Ten thousand DNA lesions per day per cell are produced." Defects that slip past the front-line defenses-DNA repair systems and proteosomal degradation-are refurbished, and damaged organelles are removed.

Also, if autophagy falls off in age, then the detritus of cell metabolism accumulate more readily. By degrading damaged organelles that generate reactive oxygen species, autophagy fits nicely into the mitochondrial theory of aging. The capacity of autophagy to catabolize whole organelles, and mitochondria in particular, may be its strongest selling point in terms of being an antiaging mechanism.

Mitochondria are a frequent target of autophagy, says John Lemasters, professor of cell and developmental biology at the University of North Carolina. "They will sort of wear out," he says. "In nonproliferating tissues like brain, heart, and liver, the mitochondria turn over every 10 to 25 days." This rate is accelerated by nutrient deprivation and glucagon, both stimulants of autophagy.

Lemasters studies specific changes in damaged mitochondria that may invite their degradation. "Autophagy becomes a mechanism to remove the ones that ought to be eliminated," he says. Damaged mitochondria might generate even more free radicals to "do mischief," which can be especially treacherous in nondividing tissues like heart and brain "where age-dependent effects really manifest themselves quite strongly." Age-related diseases of these tissues-cardiomyopathy and neurodegeneration-have been implicated as disorders of autophagy.

MOLECULAR MACHINERY The term autophagy generally refers to macroautophagy, in which an intracellular membrane forms, encircles a chunk of cytoplasm, and subsequently fuses with the lysosome where enzymatic degradation takes place. Other autophagic processes occur directly at the lysosomal membrane either via direct engulfment of cytosol (microautophagy) or via chaperone-mediated docking of damaged proteins.

Autophagy is upregulated in times of stress or change. By breaking down large proteins and organelles and feeding spare parts into protein-synthesis and energy-production pathways, the process allows cells to be temporarily self-sustaining during starvation. Another trigger is developmental tissue remodeling, such as insect metamorphosis, where organisms are "not only making new structures, but getting rid of old ones," says Daniel Klionsky, professor of biological chemistry at the University of Michigan's Life Sciences Institute. Researchers are studying the molecular regulation intensely. And by depleting nutrients, researchers can watch autophagy unfold.



The most-studied step is the elongation of membranes derived from endoplasmic reticulum to form the autophagosome. "The autophagosome is essentially made on demand," says Klionsky. Morphological evidence has long indicated that autophagy is a highly conserved mechanism. And while the genes were initially discovered in yeast, analogs of those genes are now being found in worms, flies, and mammals.

Assembly of the autophagosome requires the interaction of two autophagy proteins, designated Atg1 and Atg13, says Ana Maria Cuervo, assistant professor of anatomy and structural biology at the Albert Einstein College of Medicine in New York. "The major cascade that is involved is insulin modulating the phosphorylation of Atg proteins." When Atg1 and Atg13 are hyperphosphorylated, they cannot interact and elongation is blocked.

A kinase named target of rapamycin (TOR) controls the phosphorylation of the Atg proteins, says Cuervo. With significant roles in cell cycle,2 it's now believed to be one of the key negative regulators for autophagy. Says Klionsky, "When you are starved, TOR is inactivated and that allows autophagy to be induced."

"TOR responds to two well-characterized inputs," says Thomas Neufeld, assistant professor of genetics, cell biology, and development at the University of Minnesota. When insulin binds its receptor in the plasma membrane, it activates a signal transduction cascade beginning with phosphoinositide 3-kinase (PI3K) and converging on the GTPase Rheb. "Rheb is probably the most immediate known upstream activator of TOR," Neufeld says.

The second pathway doesn't involve insulin signaling but allows TOR to respond "more directly" to nutrient levels in a cell. "Starvation of nutrients doesn't affect PI3K, but dramatically affects TOR," says Neufeld. It's likely the older pathway, preserved from primitive single-celled organisms. "That's the way it seems to work in yeast, which doesn't have an insulin signaling pathway."

"The beauty of this autophagy system is it's completely conserved from yeast to humans," says Harald Stenmark, professor of biochemistry at the Norwegian Radium Hospital in Oslo, Norway. "So you can find basically all the components of the autophagic machinery in yeast in humans as well."

LINKS TO LONGEVITY In nematodes, researchers have linked autophagy genes to experimentally increased lifespan. Caenorhabditis elegans with a mutation in daf-2 live nearly twice as long as wild-type animals. Daf-2 normally encodes the insulin/insulin-like growth factor receptor. Inhibiting the autophagy gene bec-1 shortened the life of the mutants.3 "That's the only primary data so far" linking autophagy genes to longevity, says Levine, a coauthor on the study.

Genetic studies in fruit flies from Neufeld4 and Stenmark5 also have provided strong genetic evidence for insulin signaling negatively regulating autophagy, says Levine. "I think it's exciting because I think autophagy is potentially a unifying mechanism, which explains the diverse effects of the signaling pathway regulating cancer

Cynthia Kenyon, professor of biochemistry and biophysics at the University of California, San Francisco, is not convinced. Kenyon, who first reported the doubling of lifespan in daf-2 mutants, has since studied the altered expression of genes downstream from daf-2.6 The 50 genes that changed the most "fell into many different classes: antioxidant genes, metabolic genes, antibacterial genes," she says. "So it's certainly not only autophagy."

Other pathways have certainly been implicated in the lifespan extension induced by calorie restriction. Fasting upregulates expression of sir-2 in yeast and worms, and SIRT-2 in mice, and the resulting proteins may help mobilize glucose for use in the cell.7 At present, no one has tried to link autophagy to the sir-2 pathway, although Levine admits that she's pondered the notion.

Aging is ill defined and certainly multifactorial. The appeal of autophagy to ameliorate normal aging is its capacity as a jack-of-all-trades repair mechanism in the cell. "I believe that the induction of autophagy in caloric restriction-or loss-of-function mutation in insulin signaling-leads to increased degradation of damaged mitochondria and reduction of oxidative stress," says Levine. "And that's probably a downstream pathway that's in common to all these life extension phenotypes."

Autophagy has not been a target in aging research for long. And while Klionsky appreciates the attention autophagy is receiving now, he doesn't discount the value of working "in the shadows" before. As one of only a few labs working in yeast, he recounts, "We were going along, making a lot of progress, getting the genes identified." Then Levine's 1999 paper came out implicating autophagy in tumor suppression.8 The response was a flurry of work that Klionsky jokingly compares to party crashers eating all the food and leaving a mess. "Since then, people have solidified the cancer connection," he says. At present, autophagy is implicated in controlling neurodegeneration, myopathy, pathogen invasion, and lifespan. Klionsky adds, "Now you're seeing papers coming out in Science, Nature, and Cell."

References

1. E Bergamini et al, "The anti-ageing effects of caloric restriction may involve stimulation of macroautophagy and lysosomal degradation, and can be intensified pharmacologically," Biomed Pharmacother 2003, 57: 203-8. [ PubMed Abstract ][ Publisher Full Text ] 



2. D Secko "Sensitizing cancer through mTOR," The Scientist 18(5): [ Full Text ]  March 15, 2004



3. A Meléndez et al, "Autophagy genes are essential for dauer development and life-span extension in C. elegans ," Science 2003, 301: 1387-91. [ PubMed Abstract ][ Publisher Full Text ] 



4. RC Scott et al, "Role and regulation of starvation-induced autophagy in the Drosophila fat body," Dev Cell 2004, 7: 167-78. [ PubMed Abstract ][ Publisher Full Text ] 



5. TE Rusten et al, "Programmed autophagy in the Drosophila fat body is induced by ecdysone through regulation of the PI3K pathway," Dev Cell 2004, 7: 179-92. [ PubMed Abstract ][ Publisher Full Text ] 



6. CT Murphy et al, "Genes that act downstream of DAF-16 to influence the lifespan of C. elegans ," Nature 2003, 424: 277-83. [ PubMed Abstract ][ Publisher Full Text ] 



7. LP Guarente "Forestalling the great beyond with the help of SIR2," The Scientist 18(8): 34-5. [ Full Text ]  April 26, 2004



8. XH Liang et al, "Induction of autophagy and inhibition of tumorigenesis by beclin 1," Nature 1999, 402: 672-6. [ PubMed Abstract ][ Publisher Full Text ] 

"does anyone know of anything that causes autophagy other than rapamycin or temozolomide"

Acipimox, which targets GPR109A, the low affinity receptor for nicotinic acid, apparently does, though GPR109A wasn't deorphanized at the time. Drugs to target this receptor and other nicotinic acid receptor subtypes should be popping up soon: target for raising HDL. One could in theory use NIASPAN (prescription extended release niacin) to address this, as well.

You might want to research the effect of fasting inter- or intra-day, on protein turnover in humans and other animals, as well, and, as a subset of this, protein restriction (or at least lack of protein excess)

Best-


Exp Gerontol. 2004 Jul;39(7):1061-7. Links
Anti-aging effects of anti-lipolytic drugs.Donati A, Cavallini G, Carresi C, Gori Z, Parentini I, Bergamini E.
Centro di Ricerca Interdipartimentale sull'Invecchiamento, Università di Pisa, Via Roma 55, 56126, Italy.

Genetic disruption of insulin and insulin-like signaling pathways may extend lifespan. Hyperinsulinemia and insulin resistance may accelerate aging. The hypothesis was tested that a once-a-week life-long inhibition of insulin secretion by the administration of anti-lipolytic drugs might have anti-aging effects. Groups of 3-month-old male Sprague-Dawley rats were (a) given standard laboratory food ad libitum (AL); (b) fed AL 6 days and fasted 1 day every week (FW); © fed AL every other day (EOD), (d) fed like FW and given Acipimox (50 mg/kg b.w.) on the day of fasting (FWA) by the gastric tube. The AL, FW and EOD groups received saline intragastrically. Treatment with ACIPIMOX transiently decreased plasma free fatty acids, glucose and insulin and increased valine plasma levels, and had no long-term effect on food consumption and body weight. By age 6, 12 and 24 months subgroups were taken and the age-related changes in liver dolichol and autophagic proteolysis--which are correlated with life-expectancy--were measured. Liver dolichol levels increased and autophagic proteolysis decreased in mature and older AL rats; EOD and FWA fully counteracted these changes; FW rats had significant but smaller beneficial effects. It is concluded that life-long weekly-repeated transient inhibition of insulin secretion by antilipolytic drugs may have an anti-aging effect, additive to the anti-aging effect of a milder caloric restriction. Speculation is that transiently lower plasma insulin levels might stimulate the anti-aging cell-repair mechanism autophagy, which has longer lasting effects on cell housekeeping.

PMID: 15236765 [PubMed - indexed for MEDLINE]

Two articles that are peripheral, but perhaps of interest in the large context of the integrity of tissue remodeling during aging.

Re. #1, No abstract available, but I looked at the paper itself, and a dose of 1050mg per day of Benfotiamine, in humans (3x350mg), reversed the postprandial decline in adiponectin brought on by pre-formed high AGEP meals.

Re #2: a possible means to (possibly) safely rev up one's proteosome.

So, combined with agonists of GPR109A, and these two items, perhaps one has some chance of forestalling things a bit while one waits for "de Grey's Anatomy of Age Reversal" to be published (sorry, couldn't resist the pun, if one recalls the classic med school text).

1) http://www.ncbi.nlm.nih.gov/sites/entrez?D...Pubmed_RVDocSum


2) Rejuvenation Res. 2007 Jun;10(2):157-72. Links

The olive constituent oleuropein exhibits proteasome stimulatory properties in vitro and confers life span extension of human embryonic fibroblasts.Katsiki M, Chondrogianni N, Chinou I, Rivett AJ, Gonos ES.
Institute of Biological Research and Biotechnology, Laboratory of Molecular and Cellular Aging, National Hellenic Research Foundation, Athens, Greece.

Normal human fibroblasts undergo replicative senescence due to both genetic and environmental factors. Senescence and aging can be further accelerated by exposure of cells to a variety of oxidative agents that contribute among other effects to the accumulation of damaged proteins. The proteasome, a multicatalytic nonlysosomal protease, has impaired function during aging, while its increased expression delays senescence in human fibroblasts. The aim of this study was to identify natural compounds that enhance proteasome activity and exhibit antiaging properties. We demonstrate that oleuropein, the major constituent of Olea europea leaf extract, olive oil and olives, enhances the proteasome activities in vitro stronger than other known chemical activators, possibly through conformational changes of the proteasome. Moreover, continuous treatment of early passage human embryonic fibroblasts with oleuropein decreases the intracellular levels of reactive oxygen species (ROS), reduces the amount of oxidized proteins through increased proteasome-mediated degradation rates and retains proteasome function during replicative senescence. Importantly, oleuropein-treated cultures exhibit a delay in the appearance of senescence morphology and their life span is extended by approximately 15%. In summary, these data demonstrate the beneficial effect of oleuropein on human fibroblasts undergoing replicative senescence and provide new insights towards enhancement of cellular antioxidant mechanisms by natural compounds that can be easily up-taken through normal diet.

PMID: 17518699 [PubMed - in process]

Results in Drosophila demonstrate that promoting basal expression of the autophagy gene Atg8 in the nervous system extends lifespan by 50%



PMID: 19079287

http://www.nytimes.com/2009/10/06/science/06cell.html?_r=1

Is that right ? Do Lysosomes generate ATP like Mitochondria ?

Paul Wakfer is big on upregulating autophagy in order to extend life.

From the NYtimes article:



I talked to Ana Marie about autophagy at UABBA.

Also, impairment of lysosomal activity by the accumulation of lipofuscin is one of the reasons why Nason Schooler theorizes destroying lipofuscin will extend the lifespan of c. elegans.

http://www.sciencedaily.com/releases/2009/...91201131738.htm

interesting tidbit on autophagy. seems like another one of those "too much" and "too little" is bad on both ends of the spectrum. probably common sense, but a decent datapoint nonetheless.

At least they showed that "too little" is bad. It only said that they already knew that too much was bad. I suppose there has to be a level that is "too much", but it looks like most people are closer to too little than too much. CRONies may be an exception to that, though.

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