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see in normal aging.” A reference catalog of “normal” age-related changes in protein abundance could help researchers find specific biomarkers of age-related diseases. To identify salivary proteins that were differentially expressed in the two age groups of healthy women, the investigators collected saliva from the subjects’ parotid glands (the largest of
As we get older, our bodies undergo changes that culminate in age-associated complaints, such as stiff joints, worsening eyesight, and impaired memory. These symptoms of normal aging leave behind fingerprints in the form of altered protein expression, which can, in principle, be detected systemically in biological fluids. Someday, doctors might be able to recognize signs of normal and pathological aging simply by analyzing the abundance of protein biomarkers in a patient’s saliva. In a step toward this goal, Kiran Ambatipudi, James E. Melvin, John R. Yates, and co-workers at the University of Rochester Medical Center and Scripps Research Institute compared the salivary proteomes of young (20-30 years) and older (55-65 years) healthy Signs of aging. Researchers detect changes in protein expression women. They report their women’s saliva. results in a new JPR paper (2009, 10.1021/pr900478h). Anyone who has ever the three salivary glands). Then, they feared a needle prick at the doctor’s pooled the saliva samples from the office can appreciate the potential adseven women within each group and vantage of identifying biomarkers in fractionated the salivary proteins with saliva rather than in blood. Moreover, hydrophobic charge interaction chro“Many of the parameters measured in matography to separate highly abunblood are time-critical,” Melvin says. dant from less-abundant proteins. By “You don’t want to be drawing blood using multidimensional protein identifrom people multiple times a day or fication technology (known as MudPIT) over long periods of time. Saliva is very developed by Yates, the researchers easysyou could have the person esidentified a total of 532 proteins in sasentially spit into a cup at home, liva from the two age groups, 183 of record the time, and send the samples which were not detected in the previin for testing.” ous parotid saliva proteome. Melvin and colleagues’ work builds Melvin and co-workers identified upon a 2008 study in which 1166 promore proteins in the older age group teins in normal human saliva were than in the younger one (460 and 338 identified with MS (2008, 10.1021/ proteins, respectively). The majority of pr700764j). “In the initial salivary proproteins identified in both groups were teome study, almost all of the subjects involved in immunological protection, were young adults,” says Melvin. “Bewhich is consistent with the role of sacause several diseases that affect liva in shielding the upper gastrointeswomen, in particular autoimmune distinal tract from infection. When the orders, are age-dependent, we wanted team quantitated changes in protein to determine the background levels of abundance by G-test spectral counting, protein changes that you’d expect to they found that 293 proteins were dif-
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Journal of Proteome Research • Vol. 8, No. 11, 2009
ferentially expressed between the age groups. Of these, 88 were more abundant in the samples from the younger women, whereas 205 were expressed at higher levels in the older women. The researchers validated the relative quantitation of two selected proteins by western blot analysis. Interestingly, almost twice as many immune-related proteins were identified in the older group than in the younger one. Of the immune-related proteins detected in both groups, several (for example, lysozyme, immunoglobulin A, and lactoferrin) were more abundant in the older group. “In the older population, the normal microflora changes, so that’s one reason we think that the immune molecules and antimicrobial proteins increase in abundance,” says Ambatipudi, a postdoctoral fellow in with age in Melvin’s lab. “It’s critical to identify these normal changes in the abundance of immune-related molecules so that we can find clinically relevant markers of age-associated autoimmune disorders, such as lupus or Sjo¨gren’s syndrome [a disease of the salivary glands].” “The concept that the saliva, through its surrounding vasculature, is bringing in information from different parts of the body is very timely,” says David Wong of the University of California Los Angeles School of Dentistry. “I think this paper really sets the stage for systemic disease evaluation using the saliva proteome.” Daniel Malamud of the New York University College of Dentistry agrees that the paper could have broad implications. “Relating the salivary proteome to aging is going to be of interest to the oral biology community, to the geriatric community, and to all of the people looking for saliva biomarkerssthis is going to give them clues about where to look,” he says. —Laura Cassiday JUPITERIMAGES
Salivary proteome changes as women age
10.1021/pr9009029
© 2009 American Chemical Society
