The findings, which impact our understanding of the molecular forces that govern age-related changes, are reported in the May 23rd issue of Current Biology by Mehmet Somel and colleagues at the Max Planck Institute for Evolutionary Anthropology and the University of Cambridge.

One long-standing observation concerning the physiological decline that accompanies aging is its variability--some people age better than others. However, there has thus far been little or no evidence supporting the existence of similar heterogeneity at the level of gene expression. Lack of such evidence, in turn, gives support to a "programmed aging" hypothesis and argues against the more commonly accepted "stochastic aging" model, in which random biological events play an important role.

In the new work, researchers put to the test the question of whether gene-expression heterogeneity increases with age. Using a wide range of expression data from both humans and rats, the researchers showed that levels of gene expression become more variable with age. Furthermore, they found that the tendency toward increased variation is not restricted to a specific set of genes, implying that increased heterogeneity is the outcome of random processes such as genetic mutation.

These observations corroborate the notion that aging is underpinned by stochastic events. That said, the authors of the study point out that the observed increases in expression variation are surprisingly small, leaving plenty of room for further explanations regarding the relationship between aging-related changes at the organismal level and the underlying molecular mechanisms of aging. Nevertheless, the new results show that with the increasing amounts of molecular data available to researchers, scientists will now experience improved opportunities to answer age-old questions about the nature of aging.

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"Of course, different genes peaked in function at different times of the day," explained Dario Lemos, an OHSU graduate student in the Urbanski lab and first author of the study. "For instance, genes controlling catecholamine secretion were more active in the day with function greatly decreasing at night. Catecholamines are involved in many important body functions, such as stress and mood."

This research provides important new information regarding the complex, rhythmic, 24-hour functions of the body. The research may also impact current therapies for a variety of diseases. For instance, data gathered in this study and future studies may suggest that certain therapies be delivered at certain times to synchronize with normal body functions controlled by body clocks.

"One example is testosterone replacement, a common treatment for certain disorders in males such as sexual dysfunction and depression," explained Urbanski. "Patients receiving testosterone late in the day often complain of sleep loss. This is likely due to the fact that in healthy people, testosterone levels are lower in the afternoon and evening. As more data is gathered about body clock functions in our lab and others, we will likely learn of a specific window of time during the day where testosterone therapy is effective, but less disruptive for patients."

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