A protein implicated¹ in many biological processes also may play a role in memory, according to a study led by the University of Southern California and the National Institute on Aging at the National Institutes of Health. The findings, published this week in the Journal of Neuroscience, agree with research by a different team published online by Nature on July 11. Both studies found that mice lacking the protein SIRT1 exhibited impaired²（受损的） memory and learning, suggesting SIRT1's importance to those functions.

However, the new study also found that boosting natural levels of SIRT1 protein did not improve learning or memory in the mice, raising questions about the case for supplementing（补充，增补） a normal diet with sirtuin activators, a family of compounds targeted to activate⁴ SIRT1.

"The over-expression of SIRT1 did not improve memory, implying that increasing the amount of the protein may not enhance memory. Many more studies with different models are necessary, however, to rule this out," said co-corresponding author Valter Longo, a molecular⁵ biologist in the USC Leonard Davis School of Gerontology with a joint⁶ appointment in the USC College of Letters, Arts and Sciences.

In mice, sirtuins have been shown to affect metabolism⁷（新陈代谢） and other biological processes involved in aging. A number of studies have shown that resveratrol（白藜芦醇） , a proposed sirtuin activator³ and much-advertised "anti-aging" ingredient（原料，要素） in red wine, has beneficial effects on some aspects of health, though it does not prolong（延长，拖延） life in normal mice. However, it does improve the health and extends the life span of mice on a high fat diet.

The physiological⁸ functions of sirtuins in humans are under intense investigation⁹, with many ongoing¹⁰ studies on the effects of sirtuin activators and inhibitors on various diseases.

"This is a very controversial topic since sirtuins have been shown to be both good and bad," Longo noted¹¹. "In our previous studies [in mice and mammalian cells], for example, we showed that it was the absence of SIRT1 that protected neurons.

"So maybe there is a trade-off between protection against toxicity¹² and function such as that which is essential for learning and memory."

In the Longo group's study, mice missing the SIRT1 gene¹³ not only had cognitive¹⁴ problems, but also physical defects in their neural¹⁵ networks. The neurons of such mice had simpler structures with less branching and complexity¹⁶ – indicators¹⁷ of a decreased ability to learn and adapt.

At the other end, mice engineered to over-express the SIRT1 gene performed no better on learning and memory tests than normal mice. Their brains did not show any adverse¹⁸（不利的，相反的） physical characteristics.