Anti-Aging enzyme's secret revealed

Johns Hopkins researchers have determined how a tiny molecule normally squelches the activity of an enzyme that otherwise could help yeast, worms and flies live longer.The structural secrets they found, which are described in the March 18 issue of Molecular Cell, are likely to help efforts to design molecules that increase or decrease the enzyme's normal activity. 

The idea isn't to create a fountain of youth, say the researchers, but to help treat diabetes, inflammation, cancer or other conditions in which the enzyme plays a role. 

The enzyme, called Sir2 or sirtuin, turns on or off certain proteins by removing "decorations" called acetyl groups."Some of the proteins the enzyme turns on or off are already known to be involved in disease, and new ones are being identified all the time," says Cynthia Wolberger, Ph.D., professor of biophysics and a Howard Hughes Medical Institute investigator in Johns Hopkins' Institute for Basic Biomedical Sciences. "The idea is that specifically and carefully altering the activity of sirtuins could help fix those conditions by restoring appropriate activity levels of the specific protein involved."

For example, Johns Hopkins scientist Pere Puigserver reported just last month that the human equivalent of Sir2 is intimately involved in controlling whether the liver produces sugar when food is scarce. In people with diabetes, sugar production in the liver is constant, and targeting this sirtuin might help restore control.

 One key controller of the enzyme's activity is a small, naturally occurring molecule called nicotinamide (nick-oh-TIN-ah-mid), itself a product of the enzyme's complex chemistry. Already, scientists knew that this molecule fine-tunes sirtuin's activity by reducing its ability to remove the acetyl groups from proteins.But exactly how nicotinamide interfered with sirtuin's activity was unknown. 

One idea was that there might be two places where nicotinamide could sit in the enzyme -- one spot where it's created, and another where it just blocks the enzyme from doing its job."Our structures of the protein and nicotinamide show that this is clearly not the case," says Wolberger, whose research focuses on understanding proteins' functions by determining what they look like. "Instead, nicotinamide binds in only one spot in the enzyme."Jose Avalos, then a graduate student, found the answer by determining the three-dimensional structure of the nicotinamide and sirtuin bound together. The structure literally shows the molecule sitting in a pocket of the enzyme and also reveals how its presence prevents sirtuin from doing its thing. 

Based on this picture, the researchers altered a single component of that pocket, which made the enzyme sensitive to a different molecule."Things don't usually work out so cleanly," says Wolberger. "But in this case we made a prediction based on the structure, and we were able to prove that prediction true."Wolberger and Avalos used sirtuin from bacteria to create their structures, but the human version of the enzyme responds to nicotinamide in the same way. 

Avalos's structures clearly identify which building blocks of the sirtuin protein are involved in binding nicotinamide."Understanding the interaction in such detail can help in the design of new compounds that could inhibit sirtuin's activity or increase it," says Avalos, now a postdoctoral fellow with Nobel laureate Rod MacKinnon at The Rockefeller University. "Which one you'd want to do depends on the ailment being addressed."Molecules that mimic nicotinamide and block sirtuin's activity might be useful in treating diabetes, based on Puigserver's recent discoveries. 

Or the structural clues could be used to do the opposite, to turn up sirtuin's activity, which might restart a tumor suppressor gene called p53 that is erroneously shut off in many cancers. But those are just two examples."In the last two or three years, there's been an explosion in the number of known implications of sirtuin enzymes in biology and human health," notes Avalos.

Wolberger's goal isn't developing drugs, but understanding the details of how sirtuin works and how it's controlled, in part by understanding how various inhibitors and stimulators of sirtuin activity interact with the enzyme.

 The research was funded by the Howard Hughes Medical Institute and the National Institute of General Medical Sciences, part of the National Institutes of Health. Authors on the paper are Avalos, Wolberger and Katherine Bever.

(Source:Johns Hopkins Medicine)

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Research: Enzyme repair damaged tissues and reversed the signs of ageing

In mice, reactivating the enzyme telomerase led to the repair of damaged tissues and reversed the signs of ageing. Photograph: Robert F. Bukaty/AP

Scientists claim to be a step closer to reversing the ageing process after rejuvenating worn out organs in elderly mice. The experimental treatment developed by researchers at the Dana-Farber Cancer Institute, Harvard Medical School, turned weak and feeble old mice into healthy animals by regenerating their aged bodies.

The surprise recovery of the animals has raised hopes among scientists that it may be possible to achieve a similar feat in humans – or at least to slow down the ageing process.

An anti-ageing therapy could have a dramatic impact on public health by reducing the burden of age-related health problems, such as dementia, stroke and heart disease, and prolonging the quality of life for an increasingly aged population.
"What we saw in these animals was not a slowing down or stabilisation of the ageing process. We saw a dramatic reversal – and that was unexpected," said Ronald DePinho, who led the study, which was published in the journal Nature.
"This could lead to strategies that enhance the regenerative potential of organs as individuals age and so increase their quality of life. Whether it serves to increase longevity is a question we are not yet in a position to answer."

The ageing process is poorly understood, but scientists know it is caused by many factors. Highly reactive particles called free radicals are made naturally in the body and cause damage to cells, while smoking, ultraviolet light and other environmental factors contribute to ageing.

The Harvard group focused on a process called telomere shortening. Most cells in the body contain 23 pairs of chromosomes, which carry our DNA. At the ends of each chromosome is a protective cap called a telomere. Each time a cell divides, the telomeres are snipped shorter, until eventually they stop working and the cell dies or goes into a suspended state called "senescence". The process is behind much of the wear and tear associated with ageing.

At Harvard, they bred genetically manipulated mice that lacked an enzyme called telomerase that stops telomeres getting shorter. Without the enzyme, the mice aged prematurely and suffered ailments, including a poor sense of smell, smaller brain size, infertility and damaged intestines and spleens. But when DePinho gave the mice injections to reactivate the enzyme, it repaired the damaged tissues and reversed the signs of ageing.

"These were severely aged animals, but after a month of treatment they showed a substantial restoration, including the growth of new neurons in their brains," said DePinho.

Repeating the trick in humans will be more difficult. Mice make telomerase throughout their lives, but the enzyme is switched off in adult humans, an evolutionary compromise that stops cells growing out of control and turning into cancer. Raising levels of telomerase in people might slow the ageing process, but it makes the risk of cancer soar.

DePinho said the treatment might be safe in humans if it were given periodically and only to younger people who do not have tiny clumps of cancer cells already living, unnoticed, in their bodies.

David Kipling, who studies ageing at Cardiff University, said: "The goal for human tissue 'rejuvenation' would be to remove senescent cells, or else compensate for the deleterious effects they have on tissues and organs. Although this is a fascinating study, it must be remembered that mice are not little men, particularly with regard to their telomeres, and it remains unclear whether a similar telomerase reactivation in adult humans would lead to the removal of senescent cells."

Lynne Cox, a biochemist at Oxford University, said the study was "extremely important" and "provides proof of principle that short-term treatment to restore telomerase in adults already showing age-related tissue degeneration can rejuvenate aged tissues and restore physiological function."

DePinho said none of Harvard's mice developed cancer after the treatment. The team is now investigating whether it extends the lifespan of mice or enables them to live healthier lives into old age.

Tom Kirkwood, director of the Institute for Ageing and Health at Newcastle University, said: "The key question is what might this mean for human therapies against age-related diseases? While there is some evidence that telomere erosion contributes to age-associated human pathology, it is surely not the only, or even dominant, cause, as it appears to be in mice engineered to lack telomerase.

Furthermore, there is the ever-present anxiety that telomerase reactivation is a hallmark of most human cancers."

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