Findings may provide clues to therapeutic potential
CHAPEL HILL — More than 3,000 scientific reports are being presented at the American Society of Cell Biology’s annual meeting, Dec. 13-18, and one is a landmark study demonstrating – for the first time – that genetically altered adult liver stem cells cloned from a male rat can turn into functional adult bone marrow cells in female mice.
The accomplishment, known as hematopoietic transdifferentiation, may prove useful for tapping the potential for tissue repair using human adult stem cells.
The study is led by two faculty members at the University of North Carolina at Chapel Hill School of Medicine: Dr. Suzanne L. Kirby, assistant professor of medicine; and Dr. Nadia N. Malouf, professor of pathology and laboratory medicine.
Kirby, a hematologist-oncologist and a member of the UNC Lineberger Comprehensive Cancer Center, said the rat stem cells were injected into immunocompromised mice to avoid rejection. The cells had been genetically engineered to contain a “transgene” that confers resistance to a cell-killing drug and “marker” transgenes (beta galactosidase and green fluorescent protein) that allow detection by their color. Kirby, Malouf and colleagues in pathology and genetics demonstrated a complete “proof of concept” – namely that stem cells derived from one tissue line could be cloned and transplanted to a host where they would be supported by local environmental signals that allowed differentiation into functional new tissue.
Bone marrow contains a variety of hematopoietic, or blood-forming, cell types. In examining colonies of the mouse bone marrow cells six weeks to four months following transplantation, the researchers found, along with other types, progenitor cells that make platelets, which stimulate white cell production and fight infection. Among these were red blood cells, neutrophils, monocytes, macrophages and megakaryocytes. The rat stem cells used in the study came from a clonal cell line developed in the mid-1980s in the UNC laboratory of study team member Dr. Joe W. Grisham, Kenan professor of pathology and laboratory medicine.
“Although a few similar cell lines exist, no one else had used a genetically marked clonal cell line like this in tests of transdifferentiation,” Kirby said, adding that the new findings might be helpful in isolating an equivalent human cell line. “Ideally, you would be able to keep that cell line frozen to have available for people who might need tissue repair down the road, without having to freshly isolate new cells.”
Findings presented in November at the American Heart Association Scientific Sessions demonstrated that the same rat liver stem cell line could transdifferentiate into myocytes, heart muscle cells.
In that study, Dr. Wayne Cascio, associate professor of medicine, along with Malouf and colleagues at UNC and Duke University showed that the rat liver stem cells could transdifferentiate into heart cells by growing them in culture with either rat or mouse cardiac cells.
Although these findings were not made “in vivo,” in a living animal, the new myocytes were rhythmically beating and “were functionally integrated with the adjacent heart cells,” Cascio said. “They demonstrated intact cell-to-cell communication with cell-to-cell transmission of calcium signals.”
Cascio added that the study confirmed earlier findings presented by Malouf at the Sixth Annual Scientific Meeting of the Heart Failure Society of America in September.
“These showed transdifferentiation of adult liver stem cells into heart cells in an in vivo rat model,” he said.
Cascio said that large questions remain unanswered. “What are the signals in the microenvironment that cause stem cells to transdifferentiate into a cardiac phenotype? If we knew what these signals are, we could cause other stem cells to transdifferentiate and conform to heart muscle. These signals are now being studied by Dr. Malouf and her collaborators.”
Also unanswered, said Cascio, is how the cells become integrated and how that might occur in a real heart, an area under investigation by Malouf at UNC and Dr. Page Anderson and collaborators at Duke University Medical Center.
“Both the studies on bone marrow and cardiac cell transdifferentiation indicate how liver stem cells retain the capacity to change into other cell types, and as such might offer therapeutic opportunities in the future,” Cascio said.