New microscopic technology allows researchers to place tens of thousands of genes on 1.5-inch-square slides known as a microarray. In this case, researchers used the GeneChip Canine Genome Array, a newly available commercial microarray specifically designed for dogs and containing more than 23,000 genes. With it, they performed global genome-expression profiling to focus on the transcription (the level of genetic coding into messenger RNA) of the genes taken from five healthy dogs and two Dobermans with DCM.
In the affected dogs, 478 transcripts were significantly different from those in the tissue of the control animals. Of these transcripts, 173 were increased (up regulated) while 305 were lowered (down regulated). From this pool, the researchers identified 167 genes that may play a role in the development and progression of DCM.
The findings of the work, which was done at the University of Illinois College of Veterinary Medicine and the State University of New York at Albany, are reported in the July issue of the American Journal of Veterinary Research.
"Finding altered activity of a gene doesn't necessarily mean that it is a cause of the disease," said Mark A. Oyama, a veterinary cardiologist in the department of veterinary clinical medicine at the University of Illinois at Urbana-Champaign. "What a gene microarray tells us is more about the overall patterns of disease and how the heart responds to it. Genes that are up or down regulated may be the root cause, but we don't know that. What this experiment really does is narrow down the population of 23,000-plus genes to those that we should study in more detail."
Oyama and co-author Sridar Chittur of the Center for Functional Genomics at the State University of New York at Albany separated the 167 identified genes into eight categories to help them interpret the heart's response to DCM.
They noted that pathways involved in cellular energy production, cell structure and signaling/communication generally were down regulated, while those tied to cellular defense and stress responses were up regulated. Among the 167 genes they identified were several that may play a significant role in DCM.
The miniaturization of technology, Oyama said, has made it possible to look at thousands of genes at once, rather than the tedious, time-consuming gene-by-gene analysis required until recently. The new microarray technology, much of it developed for human medicine, he added, is allowing veterinary researchers to begin looking more closely at animal diseases, especially in increasingly popular breeds.
"It has been estimated that more than 40 percent of all Doberman pinschers are going to get DCM as they age," Oyama said. "It is progressive and invariably fatal."
DCM typically occurs as dogs reach middle age, causing the heart to enlarge and lose its strength. Dobermans, Great Danes and boxers are predisposed to the disease, but it also commonly strikes the Scottish deerhound, Newfoundland, Irish wolfhound and golden and Labrador retrievers.
"We don't know the root cause. In people, several different genetic abnormalities have been identified. We suspect a similar cause in dogs," Oyama said. "But we don't really know what's going on in the heart muscle. We also don't have a very good idea about the changes occurring in heart muscle cells once the disease starts. The body responds by activating a whole cascade of events that cause the progression of the disease. By better understanding which genes are turned on and which genes are turned off, we can begin to think about manipulating the sequence of events to stop or reverse the disease."
The researchers are now sampling a larger population of dogs so that a more sophisticated analysis can be done. "We want to understand the morphology of DCM and the pathways of genes that are crucial in the development and progression of the disease," Oyama said. "We are looking at everything that's going on all at the same time in all of the genes. Our approach kind of uses a wide-angle lens rather than a microscope. If we can better understand what the heart is doing, we may be able to arrest the disease."
The Chicago Veterinary Medical Association and the Max and Ginger Levine Research Fund supported the research.
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