David N. Leff
Editor's note: Science Scan is a roundup of recently published, biotechnology-relevant research.
Aficionados of the Monty Python cult movies, which entranced young and old in the 1970s and '80s, will remember a scene in Monty Python and the Holy Grail: The bodies of knights killed in battle during the medieval reign of King Arthur are being collected in a cart for burial. Suddenly one apparent cadaver tossed in the tumbrel yells out, "I'm not dead yet!"
Now this memorable protestation has been immortalized - literally - by two such former cult fans. Developmental geneticists Stephen Helfand and Robert Reenan at Yale University School of Medicine in Farmington, Conn., have inserted the acronymic gene for "I'm not dead yet" - Indy - into the genome of the fruit fly Drosophila melanogaster. There, their mutated Indy sobriquet designates a genomic sequence encoding a protein that can double the fly's life span.
Helfand is senior author of a report in Science dated Dec. 15, 2000, and titled: "Extended life span conferred by cotransporter gene mutations in Drosophila." Its lead author is Blanka Rogina, an assistant professor of developmental genetics at Yale.
"Indy," she told BioWorld Today, "is the same gene in humans as in fruit flies. It's present in the same places, so we propose they both have the same role."
Helfand suggested that that role - the mutations he and his co-authors have created in Indy - "may cause a form of caloric restriction. Calories either don't get absorbed or are wasted," he observed. Limiting caloric dietary intake is the only way known to extend the life span of mammals - and now, reportedly, of insects.
Their Indy mutations, Helfand speculated, "may be creating a genetic calorie restriction. It would be as if the Indy animal can eat as much as it wants without becoming obese, live twice as long as average, and still retain normal function and activity." The co-authors reported a doubling of mean life span in their mutant flies, from 37 to 70 days, and a 50 percent increase in maximal life span - equivalent to an average human life span of 150 years. The unwontedly superannuated flies showed no decrements in quality of life - remaining physically and sexually active. In tests, Indy individuals flew as well, ate as much, and courted each other with as much gusto as did their shorter-lived cohorts, and raised more than as many offspring.
Indy encodes a membrane protein that resembles a sodium dicarboxylate cotransporter, which occurs in organisms from bacteria to humans. These cotransporters function in cells of the digestive tract, placenta, liver, kidney and brain, where they transport metabolic intermediates across the cell membrane. In the fruit fly, Helfand observed, "the gene is right at the place you'd like it to be."
In humans and fruit flies alike, this is the place where the body stores and utilizes energy. The Indy protein absorbs nutrients through the gut, concentrates them in the liver (in flies, the fat body) and reabsorbs them via the kidney. "The Indy gene," Helfand surmised, "should provide direct information on the role of energy balance and aging. It offers a target for future drug therapies aimed at extending human life."
Rogina added, "At present we are further studying the mechanism of this life extension in our flies." As for extending the work to mammals, she said, "We have invitations for a number of collaborations, so we may do that."
AAV Vectors Avoided AV Hang-Ups In Delivering VEGF Genes, Restored Blood To Ischemic Hearts
Angiogenesis - the bane of oncologists, who strive to cut off the burgeoning blood vessels that feed growing tumors - could be a boon to gene therapists, for revascularizing blood-starved ischemic hearts in failure, or brains in stroke. Genes encoding vascular endothelial growth factor (VEGF), the driving engine of angiogenesis, transferred via adenoviral vectors (AV) have shortcomings ranging from short-lasting effects to immune rejection to formation of angiomas (blood-vessel tumors). (See BioWorld Today, Jan. 7, 1998, p. 1.)
Cardiovascular researchers at the University of California, San Francisco report sidestepping these obstacles in the Proceedings of the National Academy of Sciences (PNAS) dated Dec. 5, 2000. Its title: Adeno-associated viral vector-mediated vascular endothelial growth factor gene transfer induces neovascular formation in ischemic heart."
The authors created a mouse model of cardiac ischemia by ligating the animals' coronary arteries, and injected adeno-associated viral (AAV) vector-borne human VEGF cDNA directly into the affected regions of the murine hearts. They discerned gene expression continuing up to three months after initial inoculation, with no immune inflammation or angiomas. "Thus," their paper concluded, "with proper dose, AAV may represent an ideal vector for VEGF delivery."
DNAX Research Clarified Roles of CD200 Proteins In Multiple Sclerosis, Rheumatoid Arthritis Models
CD200 (formerly OX2) is a protein expressed in a number of cells and tissues. Researchers at the DNAX Institute of Molecular and Cellular Biology in Palo Alto, Calif. - a subsidiary of Schering-Plough Corp. in Madison, N.J. - suggest that it functions as an inhibitor of macrophages. These immune system cells purportedly play a key role in certain neurodegenerative diseases, such as Alzheimer's, as well as autoimmune inflammatory disorders, notably rheumatoid arthritis (RA).
The DNAX team has an article in Science dated Dec. 1, 2000, titled: "Down-regulation of the macrophage lineage through interaction with OX2 (CD200)." They created knockout mice bereft of CD200, and found these animals generated increased numbers of activated macrophage-lineage cells. Those cells showed an accelerated response to challenges such as facial nerve damage, and two autoimmune diseases that are models of human multiple sclerosis (MS) and RA.
The murine surrogate for MS is experimental autoimmune encephalitis (EAE); that for RA, collagen-induced arthritis (CIA). The co-authors propose that CD200 supplies important cellular signals that hold macrophages in check during the inflammation and trauma of EAE and CIA. Macrophages resident in the brain are called microglial cells.