Big leap in genomic screening of blood vessels from patient tissue

Aug 30 2007

Scientists have developed a new method of capturing a complete genome-wide screening of blood vessel cells in their actual disease state, advancing the potential for genetic research on the tissue responsible for delivering nourishment that can accelerate the growth of both a cancer tumor or wound healing.

The method is not just a bonus for translational research, but also has made it possible to determine that genes long associated only with cancer are also expressed in chronic wounds.

The team of scientists, based at Ohio State University Medical Center, is using laser capture microdissection to pluck blood vessels, or if need be a single cell, from human wound tissue as part of a major research initiative looking for mechanisms underlying chronic wounds.

They published a description of the research method in the Proceedings of the National Academy of Sciences scheduled for online publication this week and print publication on Sept. 4.

“We have enabled the capture and genome-wide screening of blood vessels from biopsy material regardless of disease,” said Dr. Chandan Sen, executive director of Ohio State's Comprehensive Wound Center and senior author of the paper. “It's a big leap in our ability to perform high-resolution vascular biology research utilizing patient material.”

The method is superior to previous methods of cell biology research because it allows scientists to study clinical tissue material with cell-specific resolution, said Sen, also professor and vice chair of surgery and deputy director of Ohio State's Davis Heart and Lung Research Institute. Standard research methods, such as examining cells in the lining of vessel walls, are conducted by cell culture, meaning the cells are removed from their disease environment and placed in a culture dish. The culture conditions do not mimic the microenvironment of the cells when they are in their actual diseased state.

Studies that examine biopsy tissue from patients typically study extracts of the entire biopsy, which represents a mix of numerous tissue and cell types. Such whole-biopsy extract studies do not provide precise cell-specific information, Sen noted. The new approach identifies blood vessels in the human tissue in a matter of less than five minutes, followed by robot-assisted rapid dissection and collection of blood vessels from serial tissue sections. The collected tissue material can then be subjected to genome-wide screening.

Blood vessels are critical components of multiple diseases, so their quick identification and analysis at the cellular level has broad implications.

“The main strategies of limiting cancer are to stop the vascular supply that feeds the tumor. So if you know the biology of the blood vessel feeding the tumor, you can halt that action and the tumor can no longer grow,” Sen said. “In the case of chronic wounds, the tissue can grow only if blood vessels bring food and fuel – say, glucose and oxygen – to power the healing process. “In both diseases, you need a clear understanding of vascular biology.”

The tissue screened for the study of the genetics of wound healing is supplied by a new wound tissue bank at Ohio State, which holds more than 500 samples collected from seven U.S. centers affiliated with National Healing Corp. Ohio State's Comprehensive Wound Center has a partnership with National Healing Corp., a private Florida company that manages 20 percent of the nation's wound-healing centers

“Traditionally, in wound healing, there has been no way to tell what's going on in the wound except by visualization and what a biopsy says – whether it's infected or cancerous. We're advancing the depth and level of this knowledge in our investigation,” said Dr. Gayle Gordillo, director of the plastic surgery research lab at Ohio State's Medical Center and co-author of the paper.

Current studies are ongoing to test which genes predict healing and which genes are expressed in wounds that are chronic and predict a failure to heal. The researchers are taking biopsies from clinic patients with both healing and non-healing wounds and using the laser capture microdissection to study a homogeneous cell population and run the full genome screen.

The laser capture technology allows the scientists to zero in on the microvessels, which are expected to sprout when tissue is healing. If the microvessels in chronic wound samples are not sprouting, the researchers can then turn to endothelial cells – in the lining of blood vessel walls – to see if there is a genetic basis in those cells for why wounds do or don't heal.

The first author of the study, Dr. Sashwati Roy, assistant professor of surgery, is a molecular biologist whose expertise lies in developing the method and sorting out the meaning of the data collected from the genes and identifying candidate genes involved in healing.

“One little genetic mutation can affect a person's response to medications. The laser capture microdissection represents a powerful approach to conduct cell biology research utilizing patient biopsy material,” Roy said.

“The basic assumption has been that the blood vessels in intact skin and wounds are the same. What we're seeing instead is that genes thought to be uniquely expressed in cancer are also expressed in wounds. None of these genes has been studied in wound healing,” Sen said. “So ultimately, this novel approach helps formulate new clinically relevant hypotheses. It's a highlight for patient-based research.”