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Smelling food can reduce fly lifespan

Findings suggest the effects of caloric restriction on aging stem from both less food and less of a sensation of food

By | February 1, 2007

The smell of food can affect the lifespan of flies and even partially reverse the life-prolonging effects of dietary restriction, scientists report this week in Science. These findings suggest the beneficial effects of caloric cutbacks on lifespan may not only depend on the decreased presence of food, but also on the decreased perception of it. "This work provides an important first step into understanding how neural circuits may regulate lifespan in the fly," coauthor Scott Pletcher at the Baylor College of Medicine in Houston told The Scientist. In a 2002 study comparing whole-genome expression patterns of long-lived diet-restricted Drosophila and fully fed flies, Pletcher and his colleagues found that both availability of food and age strongly affected genes encoding proteins that bound to aroma compounds or odorants, suggesting a link between smelling food and lifespan. To investigate whether smelling food-related odors could affect fly longevity, the researchers measured Drosophila lifespans in the presence and absence of yeast odorants. They found the odorants reduced lifespan in diet-restricted flies from two lab strains to varying degrees, but by as much as 6 to 18 percent in one strain. The flies' lifespans became even shorter when they received yeast paste. The odorants did not alter feeding behavior. They also did not affect lifespan when flies were fully fed, meaning that the odorants were not toxins that generally cut down lifespan. To see if losing the sense of smell could increase lifespan, the researchers used Or83b knockout flies from the lab of Leslie Vosshall at Rockefeller University in New York. (Or83b, unlike the other 62 putative Drosophila odorant receptors, is broadly expressed throughout olfactory tissues.) Relative to wild-type flies, fully-fed female Or83b-null fruit flies showed a 56 percent increase in median lifespan. In fully-fed males, the effect was smaller than in females, but males without Or83b showed an up to 42 percent increase in lifespan. Flies that were heterozygous for the mutation exhibited intermediate longevity, and expressing a Or83b transgene in mutant flies restored normal lifespan. Lifespan further increased in Or83b-null flies after dietary restriction, suggesting that odors affect longevity largely, but not exclusively, through a pathway independent of diet. "If it works in flies, it probably works in us. There are probably neural circuits of aging in humans that remain to be discovered, and these results give us a model to go forward with," Marc Tatar at Brown University in Providence, R.I., not a coauthor, told The Scientist. Previous research had shown that destroying sensory neurons in the worm C. elegans could modify aging and longevity, in part by acting on insulin signaling. However, Pletcher and his colleagues found that Or83b -null flies, with their putative compromised sense of smell, exhibited normal expression levels of insulin-like peptides. The researchers also did not see any changes in the expression of Thor, the primary target of insulin sensor dFOXO. While these results suggest olfactory regulation of aging in Drosophila may work largely independently of insulin signaling, they don't "rule out" that insulin plays some role, Pletcher said. Other pathways through which smells might help regulate aging include Sir2, he added. To further investigate the role of insulin signaling in the aging-olfactory connection, Pletcher and his colleagues are conducting experiments crossing dFOXO and Sir2 mutants with Or83b-null flies. Future research may investigate whether specific odorant receptors can also impact longevity, Pletcher added. "The olfactory system of the worm is very different from the olfactory system of the fly. The fly's is very much like that of vertebrates," Michael Grotewiel at Virginia Commonwealth University in Richmond, who did not participate in this study, told The Scientist. "The fact that knocking out the olfactory systems dramatically affects lifespan in worms and flies is fascinating, and suggests a striking conservation of the physiological mechanisms that impact lifespan across a wide range of species." Charles Q. Choi cchoi@the-scientist.com Links within this article: S. Libert et al. "Regulation of Drosophila lifespan by olfaction and food-derived odors," Science, published online ahead of print Feb. 1, 2007. http://www.sciencemag.org SJ Olshansky et al, "The longevity dividend," The Scientist, March 1, 2006. http://www.the-scientist.com/article/display/23191 Scott Pletcher http://www.hcoa.org/scott/bio.asp S.D. Pletcher et al. "Genome-wide transcript profiles in aging and calorically restricted Drosophila melanogaster." Curr. Biol., 12:R311-2 712, April 30, 2002. http://www.the-scientist.com/pubmed/12007414 Leslie Vosshall http://www.rockefeller.edu/research/abstract.php?id=156 G. Flores, "Fast track to longevity," The Scientist, March 7, 2005 http://www.the-scientist.com/article/display/15122/ M. Bucci. "Being young means feeling young," The Scientist, Feb. 16, 2004. http://www.the-scientist.com/article/display/14440 M.W. Anderson. "Sir2: Scrambling for answers." The Scientist, December 6, 2004. http://www.the-scientist.com/article/display/15122/ Michael Grotewiel http://www.gen.vcu.edu/faculty/faculty/grotewiel.html
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Comments

Avatar of: Ellen Jorgensen

Ellen Jorgensen

Posts: 2

February 1, 2007

As I was reading this article, I noticed that the top Ad in the Google sidebar on this page was for an attorney who was advertising to find clients who had experienced loss of their sense of smell after using a particular brand of nasal cold spray. I guess the Google Ads reflect key words in the article title. Unfortunately for him, the article hints that the benefits of this condition may now outweigh the disadvantages!
Avatar of: E Connelly

E Connelly

Posts: 11

February 1, 2007

And pray tell, of what importance is this to people? Smelling food will reduce our lifespan? I would like to think that scientists are working on something that will ultimately lead to something better. I can't see where this leads to anything other than a bad joke.
Avatar of: Michael Pollock

Michael Pollock

Posts: 1

February 1, 2007

In response to a previous comment: It seems to me that this research is potentially very relevant to our species. As the article points out, caloric restriction is well known to extend lifespan in Drosphila and Caenorhabditis. It would be nice to use this knowledge to extend human lives, but few people would be willing to suffer near-starvation for a few extra years (which would be pretty miserable anyway!). If the mechanism for the effect of caloric reduction can be sorted out, it may be possible to engineer other ways to activate the same pathways. But we have to understand the system first.\n\nIt's often difficult to predict which bits of basic research will be significant for human health (or anything else, for that matter) down the road. \n\n
Avatar of: Tony Edeskuty

Tony Edeskuty

Posts: 1

February 2, 2007

I found the article very intriguing. I have a question/suggestion on the following phrases: ?To investigate whether smelling food-related odors could affect fly longevity, the researchers measured Drosophila lifespans in the presence and absence of yeast odorants. ? The odorants did not alter feeding behavior. They also did not affect lifespan when flies were fully fed, meaning that the odorants were not toxins that generally cut down lifespan.? \n\nJust because lifespan was not affected by the odorants in fully fed flies does not necessarily mean that the odorants were not toxic. They could have been toxic, but the toxins were diluted because of ample nutrients in the fully fed flies. Did they try odorants which I would imagine as being non toxic such as rotting fruit.

February 2, 2007

On a previous comment regarding the relevance of this research: perhaps watching how cells in C elegans embryos divide under the microscope seemed pretty mundane and irrelevant too at the time but it eventually led to the uncovering of the genetics of apoptosis. \n\nAs mentioned before, we've got to study the on-goings in an organism before attempting to manipulate them.
Avatar of: Rodney Nicholson

Rodney Nicholson

Posts: 1

February 2, 2007

I wonder if different odours affect lifespan by different amounts? And whether some of them may even lengthen lifespan, while others shorten it?

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