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RESEARCH BRIEFS
Multivitamins Delay Onset of AIDSAn eight-year study tracking HIV-infected women in Dar es Salaam, Tanzania, has found that a simple regimen of multivitamins can significantly slow the progression of the disease. About 30 percent fewer of the infected women taking daily doses of vitamins B, C, and E reached WHO stage 4 or died of AIDS during the course of the study, compared with the group taking placebos.The study, which appears in the July 1 New England Journal of Medicine, found that daily doses of the supplements also reduced incidence of oral thrush, oral ulcers, and digestive ailments like diarrhea that can significantly impair an HIV-positive person's quality of life. The researchers, led by HSPH associate professor of nutrition and epidemiology Wafaie Fawzi and the Vincent L. Gregory professor in cancer prevention David Hunter, noted that the women's CD4+ lymphocyte count stayed up and viral loads stayed down for much longer than with no multivitamin supplements. These effects were more pronounced in the earlier stages of the disease. Women who were given only vitamin A supplements did not reap any statistically significant benefits beyond those achieved with a placebo. When vitamin A was taken along with the multivitamins, it seemed to reduce the health benefits. The WHO currently estimates that antiretroviral drug therapy is needed by more than 6 million people with advanced AIDS worldwide, but is only reaching 400,000. The organization's "Treat 3 million by 2005" initiative is designed to increase access to treatment by giving antiretroviral care to those with advanced AIDS while providing supportive care to those in earlier stages of the disease. The researchers, from HSPH and the Muhimbili University College of Health Science, say that the multivitamin regimen, costing less than $15 per year, could play an important role in extending the period in which supporting care alone is viable. --Stu Hutson
Genetic Templates Hasten Proteome AnalysisThere could be as many as a million different members of the human proteome--each one having its own way of interacting with drugs, antibodies, substrates, and other proteins. The permutations of protein interactions seem almost endless, making high-throughput proteome analysis a growing need.Protein microarray systems could tackle thousands of interactions at a time under cell-free, in situ conditions; however, the systems have yet to find wide acceptance because the proteins still have to be grown in cells, purified, and often stored in a freezer, said Josh LaBaer, director of the Medical School's Institute for Proteomics and HMS lecturer on biological chemistry and molecular pharmacology. When it comes to testing thousands at a time, the process becomes prohibitively labor intensive, and any storage of the proteins increases the likelihood that they will become denatured. LaBaer and HMS postdoctoral researcher Niroshan Ramachandran have side-stepped the need for prepared proteins by instead spotting the microarray slides with the cDNA templates for the proteins they want to study. The cDNA is far more stable, staying viable in open-air conditions for weeks. When ready for use, the researchers just add a protein-expression solution, such as reticulocyte lysate. Once expressed, the protein is bound to the site with an epitope tag. Called the self-assembling protein microarray, the system does not require any proteins to be grown in host bacterial or mammalian cells, instead users need only prepare plasmid DNA, which is much easier and less expensive according to LaBaer. Ramachandran predicts that even though spotting the cDNA requires fairly specialized equipment, one of the major advantages of the method will be that preprepared slides can be produced and activated by users as needed. The slides can be analyzed in DNA microarray scanners that are already ubiquitous in genetic research labs. Appearing in the July 2 Science, the paper describes, among other steps, how the researchers used the system to map the domain of Cdt1, responsible for binding to geminin, by arraying a series of Cdt1 deletion mutants. "What would have taken a year of graduate work with older methods only took a few weeks," LaBaer said. He predicts that the system, which is still in a "proof-of-concept" phase, will also expedite drug selectivity screens, biomarker discovery research, and protein interaction domain mapping. --Stu Hutson
Molecular Inspector Found in Cell Program For Quality ControlIn some cases, as many as 80 percent of the proteins produced on the assembly line of the endoplasmic reticulum develop defects during the manufacturing process. These misshapen proteins are tagged for destruction and shunted out of the ER membrane into protein-recycling proteasomes with the aid of the ATP-driven molecule p97. But just how this quality control occurs is still mostly unknown.Two HMS research teams have independently identified one of the ER's product inspectors, the Derlin-1 protein, by taking hints from one of the cellular world's most effective saboteurs, human cytomegalovirus. This virus slips by the body's defense system by fooling the ERs of its victim cells into thinking that class I major histocompatibility complex (MHC) chains on the assembly line are defects. Two viral proteins, US11 and US2, trigger expulsion from the ER. Hidde Ploegh, the Edward Mallinckrodt Jr. professor of immunopathology in the Department of Pathology at HMS, and graduate student Brendan Lilley observed that tagged US11 bound to Derlin-1, which then linked to a larger protein complex that ushered out the MHC. Meanwhile, a team led by HMS professor of cell biology and Howard Hughes investigator Tom Rapoport and postdoc Yihong Ye found the protein's importance by approaching from the opposite direction: they tagged p97 and backtracked their way to Derlin-1 via an assisting protein, VIMP, which they think links to Derlin-1/US11 and then flags down p97 from the cytosol to power relocation to the proteasome. The entire picture of protein expulsion is far from complete. Ploegh and Lilley found that US2 triggers MHC expulsion without Derlin-1, possibly using another Derlin protein. This could mean that the different Derlin proteins are each specially designed to deal with a different set of ER-produced proteins. In addition, US11 seems to simplify the entire expulsion process by both identifying the protein to be tossed out and associating that protein with Derlin-1. Routine expulsion probably requires an entourage of chaperone proteins to fulfill the same functions. Both teams published their work in the June 24 Nature. --Stu Hutson
Genes--Some Linked to Disease--Identified in Retinal DevelopmentHMS researchers have used gene expression profiling to identify potential therapeutic targets for retinal disease, which incurably affects nearly two million Americans. The study, led by Seth Blackshaw, who was a fellow in the lab of HMS genetics professor and Howard Hughes investigator Connie Cepko, gives patients reason for optimism. The report, a collaboration with Wing H. Wong, professor of biostatistics at HSPH, and researchers at other institutions, appears in the June 29 online issue of PLoS Biology.Cepko chose the mouse retina as a model for studying neuronal development and diseases because it contains only seven major cell types. Each type differentiates from a pool of progenitor cells at a specific time during development. To identify genes involved in cell fate choice, the authors profiled which genes are expressed at high levels as each cell type is born. They found many previously unknown genes, some of which lie in retinal disease loci, making them likely candidates for therapeutic targets. "The advent of comprehensive gene expression profiling technologies gives us a chance to get all of the puzzle pieces, rather than just a few at a time," Cepko said. "Some day, this will enable a deeper understanding of development and disease, of not only the retina, but other tissues as well." One unexpected finding is that the gene expression pattern of one cell type--Müller glia--is very similar to that of the progenitor cells. "Are Müller glia just progenitor cells that have stopped dividing?" Blackshaw asked. If so, there may be a way to make them differentiate into photoreceptors in an adult retina. This feat could help treat diseases caused by photoreceptor loss, such as retinitis pigmentosa. The researchers also found abundant noncoding RNAs of unknown function. Blackshaw, now an assistant professor of neuroscience at Johns Hopkins School of Medicine, is currently following up on the role that these transcripts play in retinal development.
Longevity Compounds Extend Fruit Fly Life SpanCompounds that mimic the effects of a calorie-restricted diet can stretch the life span of well-fed Drosophila fruit flies by as much as 20 percent and without the side effect of reducing fertility, according to an HMS study in the July 15 Nature. The study follows on the heels of research published in the June 17 Science Express, in which the same Harvard laboratory found that calorie-restricted conditions slow the intercellular chain of events that culminate in apoptosis.Calorie restriction extends the lifespan of rodents by 30 percent, presumably by down-regulating stress-induced cell death and thereby preserving individual cells in the animal. The June paper reported that a protein initiator of programmed cell death, called Bax, was held at bay by the Ku70 protein. Ku70, the researchers observed, was activated by SIRT1—a protein that is overexpressed when cells, human kidney cells in this case, are grown in the presence of serum from these animals. The team, led by HMS associate professor of pathology David Sinclair, went on to confirm that calorie restriction could also be mimicked in well-fed kidney cells by a family of chemicals called sirtuin-activating compounds (STACs). One of the most potent of these is resveratrol, a small molecule notably found in red wine. The most recent work from Sinclair's lab found that male drosophila exposed to resveratrol increased their life span by an average of 16 percent while the female life span increased by 20 percent. Similar results were found in C. elegans. STACs, which are the first calorie-restriction mimetic molecules, were found to require the SIRT1 gene for the lifespan extension. In addition, while underfed female flies usually produce fewer eggs, the egg production of the flies on resveratrol actually increased slightly. This, along with the flies' ability to maintain a normal weight on a resveratrol treatment, gives hope that the benefits of a calorie-restricted diet can be achieved without many of the side effects of a lapse in nutrition. But the researchers warn that STACs may come with their own quirky effects on other traits. It is still a mystery why animals respond to STACs, which are produced by plants under hostile conditions. One possibility is that animals use STACs as a way of cuing their own cell defense systems in preperation for an impending drop in food supply. --Stu Hutson |
