Neurology: Alzheimer's Study Maps Alternate Route to Disease Cell Biology: Yeast Ramps Up Sugar Production to Survive Cold Clinical Research: Harvard Clinical Research Group Gains Reputation for Trial Design, Statistical Analysis Women's Health In Kass Lecture, Brundtland Points Way Toward Eliminating Global Health and Gender Disparities Regulator of Protein Degradation Emerges as Anticancer Target Flaws Revealed in Study Assailing Mammograms Inflammatory Pathway Uncovered with Tie to Early Atherosclerosis   New Full and Named Professors Thier Professorship Established for Work in Health Policy at BWH or MGH Hirsh Nominated for AAMC Humanism Award, Celebration Planned for Award Nominees Student Research Displayed at HST Forum HMS Again Takes Top Spot in U.S. News Rankings Honors and Advances News Briefs   Coalition Supports Haitian Immigrants   When It Comes to Drugs, Price Is Not the Real Problem   Front Page

CELL BIOLOGY Yeast Ramp Up Sugar Production To Survive Cold Trehalose Effect Sweetens Outlook on Preserving Cells for Therapy Physicians usually worry about too much sugar, be it sucrose in the diet or glucose in the blood. But now researchers in the lab of Alfred Goldberg, HMS professor of cell biology, have found that high levels of another kind of sugar--trehalose--protect yeast against freezing temperatures. To survive the cold, yeast make the sugar trehalose, which seems to work with molecular chaperones to protect cold-sensitive proteins, according to a study by Alfred Goldberg (left), Olga Kandror (right), and co-authors Nancy Bretschneider and Evgeniy Kreydin, both undergraduates, and Duccio Cavalieri at Harvard's Bauer Center for Genomics Research. (Photo by Graham Ramsay) Other protective molecules rush in to help, but trehalose is the critical ingredient that naturally enables yeast to subsist in frosty environments, such as harsh winters and laboratory refrigerators, report Goldberg, lead author Olga Kandror, HMS instructor in cell biology, and their colleagues in the March 26 Molecular Cell. "Many students of yeast metabolism in the past had studied trehalose and assumed that it serves as a possible energy reserve," Goldberg said, "but its major role in our work is as the natural cryoprotectant that appears to protect proteins against unfolding and against oxygen radicals during freezing and at high temperatures." The Sweet Freeze For yeast, paradise feels like a toasty 86 degrees Fahrenheit (30 degrees centigrade). Cooler temperatures are tolerable, but lower the thermostat below 50 degrees (10 degrees centigrade) or to near-freezing--as Kandror and her colleagues did in these experiments--and the yeast switch to a different set of cellular processes, according to an mRNA microarray analysis. Off go the genes for growing and reproducing. On goes the transcriptional machinery to make the enzymes that churn out trehalose. Up go levels of certain versatile heat shock proteins, molecular chaperones that also protect proteins from sweltering heat. "Many students of yeast metabolism in the past had studied trehalose and assumed that it serves as a possible energy reserve, but its major role in our work is as the natural cryoprotectant that appears to protect proteins against unfolding and against oxygen radicals during freezing and at high temperatures." --Alfred Goldberg In one of the experiments, which were supported by the National Institutes of Health, the researchers let yeast adapt to the chill for 48 hours at about 40 degrees (4 degrees centigrade). Then they plunged the yeast into the brutal cold, about -4 degrees (-20 centigrade). After five days, about 70 percent of the adapted cells were still alive, compared to about 25 percent of control cells that had been frozen without adapting. All mutant cells that could not make trehalose during the adaptation phase perished in the deep freeze. "Most biologists think that life stops at this temperature," Goldberg said, referring to the transcription, translation, and protein synthesis machinery that virtually grinds to a halt in the nearly frozen yeast, except for the limited cold adaptation activity. "Clearly life goes on. These are very complex processes at zero degrees. And it happens all the time in the winter and in every lab refrigerator." Goldberg is better known for discoveries of the role of proteasomes and for development of proteasome inhibitors widely used in research, one of which was approved last year to treat multiple myeloma and is in clinical trials to treat other cancers. Several years ago, using these inhibitors, Goldberg's group reported that an accumulation of unfolded or damaged proteins elicits the heat shock response in yeast. But the expected side effects--tolerance to heat and protection from oxygen-free radicals--lasted only as long as the crucial, short-lived molecule trehalose. This sugar was more important than they had realized. Natural Preservative That might have been the end of the story for them except for a couple of related papers published in an issue of Nature Biotechnology three years ago, Kandror said. Mammalian cells do not make trehalose, but preparations with this sugar can often safeguard them outside the body, especially if enough solution can get inside the cells. One group revived desiccated human cells they had engineered with trehalose-producing genes from bacteria. Another group inserted pores that allowed sufficient trehalose into two human cell lines to protect most of them against the destructive forces of freezing. These reports inspired Kandror and her colleagues to wonder if trehalose production was a natural response to protect E. coli bacteria and yeast against freezing. "In this paper, we mainly focus on this new adaptive response," Kandror said. "We don't know yet what the mechanism of trehalose protection is. We're working on the hypothesis that a high concentration of trehalose in cells is important to protect certain protein structures from cold- or freezing-induced denaturation." Good evidence has accumulated in the last 50 years that trehalose, made of a pair of firmly bonded glucose molecules, also helps yeast endure other stresses, such as their own ethanol, excreted in fermentation. The unusual sugar is known to sustain other small organisms during drought. High concentrations of trehalose seem to protect some yeast, worms, brine shrimp, insects, and bacteria during dehydration. In fact, generations of children have delighted in the resurrective magic of the "amazing live sea-monkeys," once advertised in comic books and now found in toy stores. Water restores the tiny desiccated brine shrimp to their fully functional former selves. The phenomenon is not mere child's play. Many scientists have been working to understand and harness these natural mechanisms for medical applications. "These molecular studies in model systems are very useful to those of us trying to protect mammalian cells during freezing," said Mehmet Toner, HMS professor of surgery at Massachusetts General Hospital and the Harvard-MIT Division of Health Sciences and Technology. Taking a cue from Mary Poppins, scientists may one day use a spoonful of the sugar trehalose to store the cells and tissues of the next generation of cellular medicine, like pancreatic islets for treating diabetes, hepatocytes for liver disease, skin cells to treat burns, chondrocytes for bone and cartilage repair, and stem cells for all kinds of regenerative medicine. The anticipated future therapies will require new ways to preserve cells, which will likely mean figuring out how to freeze-dry them so they can be stored at room temperature and reactivated by adding water, Toner said. --Carol Cruzan Morton