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RESEARCH BRIEFSCloning Study Creates Tissues for TransplantationA new study led by researchers at Children's Hospital, HMS, and Advanced Cell Technology in Worcester provides the first evidence that cloning can be used to create tissues for transplantation that do not require drug therapy to prevent rejection. Using a technique called nuclear stem cell transfer, senior author Anthony Atala, HMS associate professor of surgery and director of the Laboratory for Tissue Engineering at Children's, and colleagues created cloned cow embryos by implanting skin fibroblasts from adult cows into oocytes from slaughtered cows. They next harvested heart, skeletal muscle, and kidney cells from the embryo; expanded the cells in culture; and transferred them to 3-D molds. The molds were placed in incubators to allow the cells to form tissue. The researchers then implanted the cell-mold structures back into the cows from which the initial skin cells were harvested, growing miniature kidneys and skeletal and heart "patches." These tissues showed normal morphology, and the miniature kidneys were functional, excreting metabolic waste products through a urinelike fluid. Previous studies of nuclear stem cell transfer suggested that mitochondrial proteins from the recipient oocyte used to create the cloned embryo might cause rejection. But in the new study, there was no rejection response to the cloned tissues. "The study is proof of principle that therapeutic cloning can be used to create cells and functional tissues without the threat of rejection," Atala said. Nuclear transplantation shows potential in generating functional replacement cells such as insulin-producing cells associated with diabetes, he said. It also shows promise in reconstituting more complex tissues and organs, such as blood vessels, myocardial "patches," kidneys, and hearts; and in eliminating the rejection responses of transplantation. Co-authors of the article, published in the July Nature Biotechnology and available online June 3, include Robert Lanza and colleagues at Advanced Cell Technology and other scientists.
Heart Protection By Corticosteroids Bypasses Gene RegulationAfter heart attack, high-dose corticosteroids prevent acute damage to the heart muscle. But a common long-term outcome of this therapy is cardiac rupture so corticosteroids are no longer on the treatment shelf for myocardial ischemia. Though some of the potent anti-inflammatory effects of these drugs are mediated through gene regulation, the compounds have a second, non-nuclear mode of action. In the May Nature Medicine, HMS research fellow in pathology Ali Hafezi-Moghadam at the Center for Blood Research, and James Liao, HMS associate professor of medicine at Brigham and Women's, report that it is this latter route that corticosteroids use to protect the ailing heart. Together with colleagues from Massachusetts General Hospital and the universities of Virginia and Pisa, they found that the corticosteroid dexamethasone stimulated nitric oxide synthase when applied to endothelial cells. The response was rapid and involved normal binding to the glucocorticosteroid receptor, but it was independent of gene transcription. Rather, the drug appeared to activate a cascade of kinases, including phosphatidylinositol 3-kinase and protein kinase Akt, to produce nitric oxide, a molecule known to possess anti-inflammatory, anti-atherogenic, and anti-ischemic properties. The researchers also found that enzyme activity correlated with a beneficial, NO-dependent vasorelaxation of aortic ring muscle after dexamethasone treatment and with a corticosteroid-mediated, nitric oxide-associated protection following ischemia and reperfusion injury to microvessels. Without enzyme activity, rolling leukocytes stick to damaged venules. Furthermore, when the researchers blocked blood flow to the left anterior descending artery in mice, the amount of tissue deterioration as measured by infarct size was reduced in animals pretreated with a corticosteroid. Activation of endothelial nitric oxide synthase was required for protection. Will the discovery of this novel mechanism help untangle the good of corticosteroid therapy from the bad? "It remains to be determined," write the authors, "whether modulators that preferentially activate this pathway could provide even greater benefits in cardiovascular disease." --Anne Mahon
Anti-aging Mechanism Shown in Yeast, May Be Similar in PeopleResearchers have discovered a way to genetically mimic the life-extending effects of calorie restriction--without severe food deprivation. The study was done in yeast, but the same longevity regulatory pathway--a molecular clock that determines how fast the body ages--is highly conserved in evolution. Therefore, the findings, published in the May 24 Journal of Biological Chemistry, might lead to drugs that give people longer, healthier lives. A key step in the pathway is the Sir2 protein, said senior author David Sinclair, HMS assistant professor of pathology. In S. cerevisiae, Sir2 delays aging by protecting the cell against genome instability. Sinclair's group, including research fellow and first author Rozalyn Anderson, inserted extra copies of the NPT1 gene into S. cerevisiae. This gene makes a protein required to synthesize or recycle the metabolic regulator nicotinamide adenine dinucleotide (NAD+), which controls the activity level of Sir2. One explanation of the link between caloric restriction and Sir2 is that when metabolic activity is slowed through reduced caloric intake, NAD+ levels increase, stimulating Sir2 activity. The new findings refine this theory: while overall levels of NAD+ remained steady, its rate of recycling--and thus, its availability to Sir2--were speeded up with help from extra copies of NPT1. One additional copy increased the average replicative lifespan (the number of daughter cells produced by a mother cell) by 40 percent; four extra copies, by 60 percent. "Caloric restriction has been shown to extend lifespan in almost every organism it has been tried on," Sinclair said, and is now being tested in monkeys, with preliminary positive results. Calorie-restricted animals also remain remarkably free of the common ailments of old age. --Tom Reynolds |
